If you've been having a run of cameras that scratch the negs, I'd look to other possibilities. Change labs, change film type, and make sure your camera is spotless inside. I've had cameras w/ less than pristine pressure plates that didn't scratch the negatives. In my experience, it usually comes from the lab, dirt in the camera (it doesn't take much, so tap it on the counter several times and blow it out each time) or a bad batch of film. The ringer here is that you stated that you repainted the pressure plate. So that's a potential source of issues if you haven't polished it smooth w/ a rag or something.