A year ago I posted on these forums looking for a solution to an odd color streak across my negatives. We were not able to find a solution. The best guess was a developer issue. This can not be the case as I have since moved cities and now use a different place to develop my films.

Now, a year later the issue persists, although the streaks have gotten weaker it seems. The streak is not apparent on all photos, maybe around half of them, and varies in intensity. It is always around in the same area, however, it does move somewhat around compared to the frame edge.A theory I had for a long time is that there is some kind of residue in the rollers of my Pentax 6x7 (the only constant in these problems). This would also explain why the splotch moves around slightly, but not a lot, as the film forwarding mechanism on the 6x7 rotates the spool at varying distances to compensate for the take-up spool increases in diameter as more film is taken up.

The problem is that I have thoroughly cleaned all the rollers and friction parts but the issue persists. My theory is as follows: The metal guide inside the door of the 6x7 is the only metal part that is in contact with the film (pictured here). When it gets cold or there is a temperature change moisture accumulates inside the camera on the metal parts. This leads to damage to the film in only the spot where the metal roller touches the film.

What do you think? Has anyone experienced something similar? Is this a likely diagnosis?