If you aer handy, change the seals yourself. Jon Goodman on e-bay sells the kits at a very reasonable price and it includes instructions. How are the seals on hte body?
Put a bright light inside your bellows with the bellows fully extended.. in a darkroom, check it carefully for any light leaks.. especially at the corners of the folds.
Your meter will only move if you change the amount of light coming in the lens. It is not linked to the speed n aperture at all. It is an indendant meter.. the big dial on the side is to make adjustments to null hte meter n make your readings.
Get the manual here.....
http://www.butkus.org/chinon/mamiya/mamiya_rb67_pro-s/mamiya_rb67_pro_s.htm
and if for some reason your camera won't fire or cock.. NEVER FORCE IT! Stop what you are doing n go over all the safety interlocks.
Also be sure to cock the body and the lens before mounting a lens or you will lock it up.. it will cock half way n be stuck there!
e-mail me if you have any questions?
paul