Kids toothbrush Advanced

How can I clean stains in rubber that have actually penetrated into the rubber? - rubber canning rings

As above. In the rubber industry of my mobile phone keypad, key original silver color faded (I guess the yellow is due to the oils and dirt, etc. is.) The problem is that I use all these cleaners and vinegar, Clorox, magic eraser. It also appears that the stains are gone rubbery, like the colors of rubber and their country, and not just on the surface. No idea how to remove the metal and give the keyboard of your original color, or at least to close it? Thanks in advance