Had a Nikon F3 come in with shutter capping, tried two different ways to fix the timing
First, I followed the old manual and just adjusted the first curtain spring tension. It ran okay for a day, then the problem came back. So I pulled the whole curtain assembly, cleaned the tracks with lighter fluid, and re-lubed the gear train with a tiny bit of Moebius 8000. That was the fix. The spring adjustment was a band-aid, but the real issue was old, sticky grease. Has anyone else found that a full clean beats a quick adjustment on these older metal shutters?