I think I may have found the problem? On the back left side, part of it is warped, evidenced by the non-parallel lines. When I push on it, it flexes inward, unlike the opposing side, which is both parallel and snug. Could a leak here lead to the examples I posted? I'm unsure because the film is rolled up in the rear of the back, not "open" like it is closer to the dark slide.

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