I don't know if this will work on a CD-R, but I just used Brasso (has a very low-level abrasive) to clean some scratches off the back of my OS 9 CD that wasn't fully loading (loaded almost all of the way before reaching a part it couldn't read, and saying so.) It worked well; I was able to load the entire OS without a hitch immediately afterward. Again, I don't know if this is too much for a CD-R disc; use at your own risk!