Exposure number window too pale

This Semi-Leotax is in very good condition and takes tack-sharp pictures, but it has a very pale back-door window which has light leaked in the past. Not sure if they were made this way, with a cheap quality plastic, or if it has faded over time.

Picture 1, picture 2.

I would like to find an easy way to fix this without taking it apart (I understand taking everything apart is the "right" way to do it like the pros, but it's also how I've broken a lot of gear).

Could I just paint it with some red nail polish or stained glass varnish paint? Has someone tried that?

I brought a small sheet of red lighting gel from ebay and cut a piece to fit over the existing window. I have 3 cameras with counter windows and have put this on all of them.