Hi there, I'm the chap who wrote said repair manual. Basically it sounds like a problem with the slow speeds escapement interaction with the main shutter escapement. It could be as simple as a drop of oil or it could be that a new part is needed. My recommendation would be that, if it is a otherwise excellent camera then approach ARAX http://www.araxfoto.com/ in the Ukraine to see how much the repair would be. If the camera has seen better days then there is nothing to lose in attempting a repair - you should only need to go as far as removing the focus screen, mirror and internal baffles/floor to get clear access. By cycling the shutter you should be able to see what it catching up.

Cheers,

Steve