Cal 1570 setting lever screw replacement advice

[Fioran0]

Hoping anyone who was delved into the vintage mechanisms might be able to help with info on replacing the setting lever screw (stem retaining screw) from a cal 1570.

Watch started misbehaving over the holidays. Crown would need an additional pull/push to get going after setting hands. Escalating firstly to extra finessing and then finally crown/stem just coming out all together.

Opened up to find stem screw loose but unabe to tighten. Pulled dial and found setting lever underneath loose too. Small bit of crumbly material in the setting lever which cleaned out ok to leave a hole. But no threads of any screw protruding to reattach. Assuming its either sheared, or been short for a while and ive been riding luck.

Wanted to ask a couple of questions. First to check sanity. Second a whats next.

Am i right in thinking that the stem securing/setting lever screw is the same thing. The screw threads from behind into the setting lever to hold in place. Tightening pulls the setting lever against the stem to lock. Loosening does the opposite.

If above correct. How does one replace the screw. Im 50/50 on whether its captive underneath the automatic winding bridge - or indeed the plate below that. Or whether it should just come out as is by giving it a push.
Would rather ask than go exploring. Especially since replacing screw/lever from current position looks ok. Stripping further something Im less keen to try.

[woolshire]

To replace the detent screw one needs to remove the barrel bridge to replace it. That involves removing the automatic works, the ratchet wheel, the crown wheel, and then remove the barrel bridge (make sure you release power first!). You may also need to remove part of the keyless works from the other side, depending on if there are still remnants in there.
A watchmaker could replace it in 20-30 min but you may wish to fully service the watch if it’s been a few years…here’s the screw you need: