I've searched here and elsewhere online but have read no obvious solutions...
A recently acquired(gunbroker) 686-5 has a loose thumb latch/cylinder release.
I removed the screw, removed the thumb release, cleaned both, cleaned the slot, and reinstalled. Still wobbly.
The black (post?) that accepts the screw is slightly wobbly while the release is off of the gun.
I have a 617 and the release is tight.
Any ideas?

That piece is called the bolt.
The threaded stud is, I believe, pressed into it.
Likely worked loose. Not a common problem, but certainly a possibility.
If that's the case, I'd just replace the bolt. Not an expensive part and easy to find.
Its #22 215310000 $22.90 BOLT
S&W, Midway, Brownell, Jack Frist, etc.

__________________
-jwk-
US Army '72-'95

I imagine I'll have to pull the side plate off to replace?

That is correct.
Damaging the sideplate is likely if not removed in the correct fashion.
Read this first:
Removing revolver side plate.

__________________
-jwk-
US Army '72-'95

Side-plate off to get to the guts. The hammer has to come out. The bolt is behind the hammer and spring-loaded from the rear. You will have to remove the main-spring to remove the hammer to get to the bolt and of course....the hammer block will fall out of position when you remove the side-plate. When you remove the bolt.....press it back and up from the front paying close attention to the plunger and spring inside the rear of the bolt. If this is your first time to go into one....don't let anything scare you....we all had to learn. Just keep a close-eye on that spring in the rear of the bolt.

I little trick I use at work sometimes with wiring harnesses or air-brake valves, etc:

Take a couple pictures of the guts before you touch anything.
Then you have a visual reference to go by for reassembly.

I'm going to give it a shot. I ordered a new bolt from Jack Frist.

Any you tube videos you'd suggest?

I've noticed the exact opposite with my newly acquired pre-lock 625-3. The cylinder latch is pretty stiff, noticeably harder than it should be. Pushes half way easily then kinda hits a hard spot. Almost a two step process to push the latch, first part easy then really have to push hard to get it all the way. Should I take the screw and then the latch off and clean from the outside? Not really wanting to get into the guts at this point.

I wonder if the obstruction is in the frame or the cylinder itself.

Have you tried the catch with the cylinder open to take it out of the equation?

Be aware that there is a spring & plunger on the rear of the bolt, and when you lift out the parts may launch somewhere unknown if you do not capture. Just lift/work out with the right hand and cover with the left hand. While you have it to that extent of disassembly it is a good time to clean and lube. Don't go overboard on lube, S&W are made to run without excess lube.

__________________
H Richard
SWCA1967 SWHF244

FYI Brownell has exploded views on their web site that should help you located and understand how and were all the parts go.

It not that difficult.

Good Luck