I hear what you are saying.

I was under the impression that all he needed to do was get the wax off the rubber, thus my suggestion.

I have had success doing this with a number of protectants, my favorite being Turtle Wax Black Chrome, unfortunately now discontinued.

I have used back to black, but I would agree that on damaged rubber, i.e. oxidized, it does not last. In addition, I have found back to black to have a very strong solvent in it, and don't recommend it as my first choice.

If that does not work, I would agree that a more potent approach is in order, as in the one you suggested. I found another product, Black Again, (from properautocare.com) that worked on undamaged plastic and vinyl.

My example use was: I have a 2003 SL500... this has a socket in the front left corner of the passenger seat for a really nice, big cupholder. When you don't use the cupholder, a little plastic cover fits over it. Well, in my Designo edition, the interior plastic on the seat is dark, matte black. The cover appears to be a little different black color, lighter, and it looked out of place. I ordered another and it was the same color. So I used this stuff, which you spray on, and then let bake in the sun. It darkened the piece just exactly right. A small thing, but worked great, so I have added another chemical to my "bag of tricks".

Greg