I have not found a way to bring back faded/browned out light covers,
tried putting them in bleach, no go!
I did find some locally, I painted the top(s) with red gloss nail polish.
You want your roll over buttons to move freely in the hole(s).
I also found, that if I adjusted the contacts under the roll overs
carefully, the ball(s) would roll over them nicely with out deflecting their
movement; i.e. the contacts just make contact with a slight/light press!
As far as the actual roll over buttons, I like the Yellow to be nice and glossy
as well as the Red!
Terry K