I have a problem with a stuck shutter on a Retina IIc. (The cocking rack is fine). I’ve taken off the front assembly down to the timer ring. When I cock the shutter using the cocking ring everything is OK. However when I cock it using the film advance, the lever at 12 o’clock( which is supposed to engage with the cocking ring until the shutter is fired) shifts upwards as soon as the film advance lever is released: so the cocking ring shifts back too far and the shutter release is blocked. I'd be grateful for any advice.