Hi,

A similar type of plastic (for lack of a better word) is used for other applications -- one is automobiles. The wear or discoloring is not unuaual for some with the oil in hands that does this.

Since from what you describe can't be ruined any further -- you can use a product called for example Black Chrome polish -- used for the black appointments on cars such as on sides of doore, bumpers, around some trim, etc. (check out a well stocked Auto Supply or parts store.

One procduct Black Chrome Polish by turtle was should do a decent job of getting the color back. They may have a pre cleaner -- if so get that, then use the polish. I have seen it do a good job on many things that people salvaged -- saved from being thrown away.

good luck