I was out shooting yesterday with my Rolleiflex 2.8 E. About half way through a roll of Tri-x I was advancing the film. About halfway through advancing to the next frame the crank stopped and would not move forward or backward. I got the film out in the darkroom and now the crank will move forward and backward but it does not seem to be cocking the shutter. The shutter does not work at all. Any ideas of what happened? Who is the best to send it to for repair?