DWThomas: The scans in my original post are not looking through the emulsion side. They are reversed (normal) -- whatever that's called. So I suspect Alex Muir is right. There is a leak towards the bottom of the dark slide slot. Also, the seals shown in the shot you posted here are intact, and look the same in both backs. Maybe the best solution is to get one of John Goodman's Interslice kits and just over-seal the back, hoping that solves the problem. Meanwhile, I may just put a fat rubber band around the dark slide slot area after I've loaded the back and pulled out the dark slide, then hope for the best! Thanks to you and Alex for your help with this.