Yep, the single side (left) manual safety assembly has a smooth/flush-with-the-slide end on the right side.
The top of the sear release lever indexes off a surface of the safety/decocker assembly as it's rotated in the slide for decocking. Replacing an assembly sometimes requires that a new sear release lever is fitted to the frame so decocking timing remains within normal specification.
Armorers used to be taught to check this by slowly manipulating the decocking lever(s) on a fully assembled EMPTY pistol (with an EMPTY magazine inserted in the grip) and checking to see when the hammer did (and didn't) fall. Additionally manipulating the lowered (decocked) hammer to check for full downward movement of the decocking lever(s) after decocking occurred was also involved.
Spurless hammer models required using the end of a wooden armorer's block to catch and pull back the decocked hammer (on the older flashchromed hammers with serrations), or else the end of one of the larger pin punches was pressed into the gap under the bottom of the left lever within the recessed space in which the lever moved, as a gauge reference (this was needed when the MIM spurless hammers came without serrations).
Nowadays armorers are taught to use a set of 3 'gauges' to check for proper decocking timing. The shanks (non-cutting end) of 3 different size numbered drill bits are used as the 'gauges' (held in the same recessed area of the slide under the bottom of the left lever). It's quicker and easier to use the gauges ... and it's an easier technique to teach to new armorers in the short 3-day class than trying to get them to properly 'eyeball' the tolerances while slowly depressing the levers and checking for hammer fall.
Short answer?
Replacing the manual safety assembly may require a new sear release lever being fitted in order for the decocking function to occur as intended.
FWIW, sometimes a new sear release lever might eventually have to be fitted in a well-used gun after a lot of decocking ... (I've had to replace a few in older guns over the years) ... or else in one where the original lever was fitted too far on the 'wrong end' of the tolerance range when the gun was produced.
Fitting the levers is relatively simple as far as such things go. The bottom of the lever's 'foot' is filed until it provides for normal functioning in the specific gun.
The trick is to make sure the surface is filed evenly and the original angle is maintained.
The time consuming part of fitting a new lever comes from having to strip down the involved parts from the frame just to make one or two passes on the lever with a file, and then reassembling the whole gun in order to check the timing.
The older levers were often pretty long in the required dimension compared to what they eventually needed to be when fitted and installed in most guns, while the newer production levers seem to be much closer to what they need to be and seem to require less fitting. Naturally, the closer overall tolerances of the newer production guns makes it easier in this regard, too.
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