I'm having a problem with my Nikon FM and I can't tell if it's a shutter malfunction or a flash sync problem. I recently started seeing a dark area on one side of the frame, not quite a black band and usually at the top of the frame. Shutter is at 1/125 which is the rated flash sync with this camera, motor drive also on. I'm using studio strobes, Excalibur 6400's. I'm thinking just go to 1/60 second on the shutter and this may clear the problem. I know the strobes have a flash duration of only 1/200 at full power, probably less at reduced power, could this slow duration cause a sync problem with the 1/125 shutter speed?