Well here is problem I've never experienced before, which I guess is a good thing! I recently purchased an original Mamiya RB67, mint condition in appearance, from an ebay auction and never got the chance to use it due to my insane work schedule. Now, a month later I made the time to run a couple rolls through it and check out the results. Everything looked good except for the last of 5 rolls. Good old #5 only had four frames exposed. Frame numbers 2,3,4 and 7. The rest appeared completely blank.
Now all of theses rolls were taken in my studio, so as to have a controlled lighting situations. It sounds as if the mirror is a bit sluggish lifting. Everything feels smooth upon pressing the shutter release and the camera following through. Just slower than it should. I've removed the lense and the back and watched the whole process and a couple of times the mirror didn't even make it to the top of the run! It was about a quarter inch from the "up" resting position. I gently touched it and it raised the final bit. When I say gently I mean that I honestly could have breathed on it and it would have given the same results.
Sounds to me like it just needs a lube job?? If this be the case does anyone have any recommendations as to who to go through?