Blue Horizontal Line in Negatives

[exaktauser]

I just started using another Exakta VX. The prints show a thin, horizontal line in almost every frame. The line is more visible the darker the image. I looked closely at the negatives and there it is! What could be causing this problem?
The camera interior is clean and light-tight, the film advance and rewind mechanisms work as they should. Any Ideas?

[ozphoto]

Could be grit caught in the light-trap of the film cannister. Back in my lab days, many ladies would pull their film from the deep, dark recesses of their handbags, sans container, and I'd have to spend time either cleaning the dust away with a toothbrush before loading, or destroying the darned thing in a darkbox and transferring to a processing cannister so they didn't get scratched. (Oh and some guys used to pull them straight out of their pockets on their jeans - same problem, just different garbage needing to be removed.)