Firstly, hi im new lol

I have a question. I have a pair of bowers and wilkins 602's. Had them years now and they are great. Only problem i have is that over the years the rubber around the main bass speaker has gone light in colour and i was sondering if there is anything i can buy to rub on it to restore it to better condition. The rubber is fine, just looks faded. Dunno why they have gone like it tbh.

Any ideas guys?

Pic here so you know what im on about lol