thanks a lot dehk, I've just gone through what you said - all the parts seem to be moving freely, as you suggested it is not going down far enough to trip it. Nothing seems bent, and nothing seems like it needs any lube. The part of the linkage directly connected to the shutter button shaft is moving freely and comes in contact with the lever on the lens assembly, but does not push it far enough to trip the shutter. When I do it manually, it fires easily and smoothly. There's one adjustment screw that I've found (in the pic in the first post) but no luck finding anything else that can help me out.
MFstooges - I actually thought that might be the case but it definitely seems free of the front cover. It seems almost as though the lens cover/assy is sitting too low (vertically, if you know what I mean), however there's no way it can move upwards.
Thanks a lot both of you, I'll keep trying and let you know if I have any progress.