With the slide resting on the sights, upside down on a flat/firm surface ... (My description is done with the slide upside down, the right side of the slide facing me, with the muzzle pointing to my left)
Holding a pin punch in each hand (1/8" works fine for this part), I depress the firing pin safety plunger with 1 punch while pushing the other pin punch against the back of the firing pin, and then release the safety plunger when the firing pin is fully forward, which traps the firing pin partially forward.
Yes, it will not be far enough forward to remove the manual safety assembly body (called a "selector" in the OP's post), which is why you use a long non-tapered 1/16" pin punch to complete the removal.
This is done by simply inserting the 1/16" straight pin punch into the space behind the firing pin (
leaving the manual safety lever in the forward/ready-to-fire position) ...
... until it reaches the end of the firing pin (which you can't see), which is when you push the firing pin a little bit more forward, until it can't go any farther forward, holding it there with the punch ...
... and then push against the
right side (end) of the manual safety body until the thin pin's shaft is "trapped" against the inside of the slide (you're not going to have to push it far) ...
... Then pull the pin punch out, continuing to push the manual safety body to the
left side of the slide (away from you, if the right side of the slide is facing you as it's sitting on the bench) ...
... Taking care to carefully reach a finger over the bottom of the slide (since it's facing "up"), to trap the manual safety body plunger as it becomes exposed with the safety body's movement out the left side of the slide. Don't let it go flying (may, or may not, but trap it anyway).
Depress the firing pin safety plunger to release the firing pin & spring.
Badly fouled firing pins which don't fly free when the firing pin safety plunger is depressed (to release it) may have to be carefully pulled from the channel (while the firing pin safety plunger is depressed), and then the firing pin spring may have to be pulled out separately. I use the end of a paperclip, carefully bent into a short hook, to catch the end coil of the spring ... while depressing the firing pin safety plunger and pulling the spring from a nasty channel.
Care must be taken to avoid using the wrong kind of cotton swab inside the firing pin channel. Cosmetic swabs may come apart. The gunsmithing swabs stay together better. Use a strong light to make sure there aren't any fibers or parts of the swab left inside the channel after cleaning.
Reinstallation is mostly the reverse, with an exception ... (and don't forget to install the body plunger and its heavy spring) ...
As the manual safety body is pushed into the left side of the slide, it will reach a point where the firing pin (trapped in the forward position by the firing pin safety plunger) stops the manual safety assembly from moving. If you look at the right side of the manual safety body (shaft), through the hole in the right side of the slide, you can see the firing pin as the manual safety body butts up against it.
If the manual safety is an ambi style, and the left side lever is positioned just right (slightly down), the end of the pin can be caught within the machined slot on the right end of the manual safety (for the ambi lever). This actually makes it easy to depress the firing pin that little extra bit needed to complete installation of the manual safety assembly. Using the end of a 1/8" pin punch, the firing pin is simply levered forward (I push the side of the tip of the punch against the firing pin) enough to clear the manual safety (as the manual safety is pushed past it) ...
... as the manual safety reaches a point in its movement, a sharp corner may bump up against the inside of the slide cuts, and it can be freed by a gentle wiggle (you can look into the right side of the slide, through the round hole, and see this). As the manual safety body slides into position, I twist the left manual safety lever "down", as if I were depressing the lever to decock, and the body plunger will easily slide into the machined recess where it normally moves.
I release the firing pin by depressing the firing pin safety lever.
Then, holding the firing pin safety lever depressed with 1 hand/pin punch, I use another pin punch (in my other hand) to push in & out on the end of the firing pin, to confirm it has normal freedom of movement and spring tension.
Of course, it's also a good idea to check the firing pin safety plunger function by pushing on the firing pin,
without also pushing on the firing pin safety plunder, to make sure the firing pin is blocked and can't protrude through the breech face hole.
If the gun has an ambi lever assembly, install the spring, plunger & lever.
DO NOT MIX UP THE BODY PLUNGER & SPRING WITH THE AMBI LEVER PLUNGER & SPRING!!! Doing so can result in the gun "decocking itself" and putting itself on-safe when fired. The light ambi lever spring is painted light blue and is significantly lighter than the body plunger spring (which is unpainted). Also, the plungers are different, and the ambi lever plunger mistakenly being put into the body assembly could result in heavy friction and resistance (and marring the inside surface of the slide where the body plunger rubs).
The ambi lever plunger in newer 3rd gen guns has a wide head. The body plunger has a round head and a "shoulder". In this picture the ambi plunger & spring is on the right.
In early 3rd gen guns, the ambi lever plunger has a narrower flat head and a machined shoulder, making it look almost similar to the body plunger ... except under close examination the plunger's head was still flat, not rounded. This also meant that the older ambi levers in 9/.40 guns had smaller plunger head holes (so a newer style ambi plunger won't fit in them) ... except for .45's, which I think may have had the wider headed ambi plungers either earlier, or all along (I'm on the road and don't have access to my older manuals and notes
).
The decock-only assembly requires an additional step toward the end of the assembly's insertion into the slide.
The end of the large spring (wound around the body) must be correctly positioned into the small recessed hole under the left side lever where it's normally captured and rests. I use a thin pin punch to nudge it over the hole, and then gently press the assembly the rest of the way into the slide, watching to make sure the end of the spring went into the hole (and wasn't moved out of line with the hole by any twisting of the assembly body/lever). If it doesn't go into the hole, but is just trapped within the shallow step of the machined cut surrounding the hole, it's not installed properly (and the end of the spring might get bent).
All of this is a lot easier to do and try to write down, however, it does require some knowledge and practice. Once someone is familiar with how to do it properly, it takes less than 1 minute to remove the manual safety assembly and firing pin. This includes removing the ambi lever from an assembly that has one (1/16" pin punch is used, reaching into the lever's hole to depress the plunger while sliding the lever forward).
In older .45 slides there was a machined groove on the outside of the slide, angled just forward & down of the ambi safety lever. This was so the ambi lever could be lowered and removed (after which the manual safety assembly and firing pin could be removed in the normal manner). The 9/.40 slides didn't require/have this extra machined groove for ambi lever removal.
The newer production .45 slides don't have (or need) this machined groove, and the ambi levers are removed in the same manner as in the 9/.40 slides (meaning they could be pulled out of the end of the manual safety body, removed forward, while the levers are in the forward/ready-to-fire position).
If you have an older .45 slide ... modified to accept the spring-loaded, decock-only option ... removing the ambi lever can be ... interesting. The ambi lever must still be removed from the down/lowered position, but you have to hold the other side's lever down against spring tension while dealing with removing ambi lever. This can
really make it seem like a 3rd hand would be handy.
BTW, when the spring-loaded, decock-only assembly is installed in 9/.40 guns, the ambi lever must be the .45 lever. This is because the .45 ambi lever has an additional bit of metal on the inside that keeps the body assembly from shifting inside the slide and interfering with the firing pin's freedom of movement.
This picture shows the tip of a pin punch pointing to the extra metal (spacer tab, if you will) on the .45 ambi lever, which butts up against the outside of the slide and keeps the manual safety body from shifting.
There are some things that can create problems for the hobbyist unfamiliar and untrained to actually work on these guns.
FWIW, removing and reinstalling the rear sight is a subject of its own. In the 9/.40 slides the exposed plunger springs can easily be cut/clipped, bent over or otherwise damaged as the sight base is reinstalled. I've seen guns which had damaged plunger springs under the rear sight. In the .45 slides with the plunger spring cover plates it's easier to avoid this happening, but improperly pressing the cover plate onto the 2 plunger springs (different heights/tensions) can present the potential for 1 of the springs to get bent over and trapped underneath the plate. I don't like to remove rear sights except for repair (replacement), or in the event a gun has been submerged and contaminated (silt, sand, grit, etc, and salt water can corrode things).
Also, spraying some aerosol cleaner up inside small spaces inside the slide may result in condensation and trapped moisture. Not generally a good thing. Even some air compressors can blow moisture under some conditions. Might even trap debris that can't easily "flow" out of the small openings.