On the 645 backs there are two long rollers on top and bottom of the front opening. This is on the back, not the insert. They run from one side to the other, apparently the film passes over them on the emulsion side. I've thuroughly cleaned them but one of them on one back has a little nick on it. It has scratched some of my negatives. (Isolated to this particular back and the position on the negative where the scratch marks are.) Any suggestions on how to fix this or should I just toss the back and get another one from KEH? The assembly can come out for replacement but I don't know if it is economically worth doing, if the part could be found. I was thinking some sort of polishing or buffing could take the nick out but am concerned about ruining more film.