Note that the case screws for Speedmasters don't affix the movement to the case. They clamp it to the enlargement ring (movement spacer) so they don't really hold the movement rigidly in the case. The inner anti-magnetic cover fits over that enlargement ring, and the case back presses on the cover - that is what holds everything in place firmly.
If the inner cover is deformed slightly, it may not be providing contact with the case back, so that may be allowing the movement to shift around on winding. If you have fitted one of those aftermarket display case backs, then the spacer they provide has to be just the right fit - if it's too loose again it will not contact the inside of the case back and hold everything in place. I know the seller for these has sometimes had issue with the spacers not being the right thickness.
Hope this helps.
Cheers, Al
Click to expand...