What brand of film holders are you using? I ask, because if you're using Linhof brand film holders, they load slightly differently than 'normal' film holders. Also, are you using 'newer' plastic film holders like Fidelity, or such, or if you're using older wooden Graflex brand film holders, that can make a big difference. It's fairly normal for a film holder to have a slight amount of play right to left even when it's sitting against the camera back properly. Do you have your film holders marked so you can tell which holder the fogged film came out of? Is it always the same one? If you don't have your film holders marked, I would suggest that you mark each one with either a notch code, or a number on a small piece of film mounted so it marks the film, such as the ones in the images attached to this message. Once you have a way to tell which film holder is fogging the film, you can go further to investigate the fogging.

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