This may sound trivial, but it's bothering me more all the time...

The volume **** on my radio has darkened from frequent adjustment. It's not like I go around with filthy fingers or anything like that, but it seems like it looking at that **** compared to the other ****.

I took the **** off and scrubbed it with all kinds of cleaners with no real improvement. It seems the rubberized surface has absorbed dirt to the point of no return.

Does anyone else have this problem? And does anyone know of a way to make it look new again?