I own a C1 and am having problems with my 8x10 back leaking a bit of light around the film holder. My model has a bit of felt on the fixed section of the back that the film holder rests against. It looks like this felt was added to the camera. My 4x5 back for this camera is similar, has no felt and doesn't leak.
My question: Is the 8x10 back supposed to have felt or should the film holder sit against the metal?