I pulled my Mamiyaflex out of the closet the other day, only to discover that the shutter is ... grumpy. It fires on the highest speed, but on anythieng below 1/100th, it either sticks, or makes a painful noise; it doesn't seem to be timed correctly. Theev B setting does not hold the lens open. The lever that triggers the shutter also does not pop back up after the shutter fires; I have to pop it back up before I can re-cock the shutter. Does anyone have suggestions on repairs? DIY? Is there somewhere that I can get this done?