dark spots on film edge

I've had a few rolls of film with dark spots here and there on an edge. I thought the problem may have been a light leak while processing the film, but it sounds more like with the camera, doesn't it? I've not seen the same issue with my 120 film.

I'm shooting an FM2.

I think I'll load film in my F100 and the FM2, shoot, then process them together. THat will tell me for sure if the problem is the camera or the processing. If it's the camera, is that an easy enough problem to fix?

Thanks.

Janet

Shooting a roll in each and processing together is a good first step. Could possibly be a gazillion things, but light seals along the back door are worth checking. If they're gooey, time for new ones and yes, that's plenty easy.

Jo