When loading film into one of my Canon F-1Ns, I noticed some type of line or mark that runs across the shutter curtain. It is straight and runs just above the center area, and it does not appear to be a deep scratch--just some type of scuff. It even looks like it could be a some type of line of dirt that has run across it. I have thought about trying to lightly wipe it with a clean swab (or something else?). I have successfully cleaned a number of camera mirrors (which is supposed to be somewhat risky). Any opinions?