Rust color removal from Final Fantasy VII fluorescent display overlay?

I I have been restoring this Final Fantasy VII lighted display. As can be seen on the picture below, it has a few rust colored marks. The only one that really bothers me is the long one under the letter "F". It is actually a tear that has what seems to be a permanent rust colored stain. Any ideas on how to at least fade it somewhat. I've tried rubbing alcohol, an eraser, and even a Magic Sponge to no avail. There are a few more rust colored marks located under Cloud's arm which is holding the sword, but they don't bother me as much.