how hard is the rubber? If its still hard, clean it, then use a product like plastic renewzit for returning gloss to plastic. go slow, it can work. I have brough other plastics back from oxidized hell to a nice gloss.
OR, if it is clean (not soaked in armorall or the like) you can shoot it with a high gloss clear coat enamel and that will return the luster. The downside is doesnt last a long time, but it is easy to redo.
If you try either of these start somewhere on the wheel where it is least noticible and verify the technique before committing the whole wheel.
