Assuming the views above are "normal," looking through the base side, I'm thinking this is appearing opposite the dark slide slot. One of the troublesome areas is near the upper part of the back shell opening, and between the roller and the spool, not in the film gate region (and more likely to extend into the rebate.) That is the light leak is hitting the frame before or after the frame being shot. This is based on my own dubious experience and not any thing I've read somewhere.
There are some small blocks of foam shown in this shot that seem to be important. Unfortunately I don't have any shots of a new, out of the factory back, so I'm not 100% sure what good and proper seals should look like. Backing up in the hierarchy on that page will show what a back with almost totally missing seals looks like! You could experiment with some black tape to try and localize the problem.
Last edited by DWThomas; 03-24-2013 at 06:12 PM. Click to view previous post history.