I just took apart the back of a sigma 24mm 2.8 filtermatic (minolta mount) for no reason other than I wanted to. I can put it back together such that it mounts, but the apertures no longer click at the stops, and the auto-coupling spring pulls the aperture ring back if you put it above f/5.6.
You may have dropped the small ball bearing that presses against the aperture ring. It's usually just free floating backed by a sheet metal spring for tension against the body.
Did just that. Thankfully I had a crappy quantaray 70-210 lying around, cannibalized it for the ball bearing. The clicks are a little softer, but it's no longer broken.
Glad everything worked out, next time work within a low edged plastic box, or lid with a lip, and line the bottom with a soft lint free cloth to prevent bounces.
Soft clicks just means ninja mode activated haha. Also did you happen to get images of the filtermatic innards? Ive never had one but was always interested on how they positioned the filters/gels.