Skip the paper towels. You can try #7 or Windex for cleaning but to really condition it I would use the Endurance gel. Put some rubber gloves on (the stuff can be tough to wash off your hands) and apply to the trip by hand. That is to say you massage in the gel with your finger(s) until you start seeing a positive result. This trick also works with faded door handles. It may take some time but just be patient and precise and it should work. Once you have it thoroughly blackened up, let a good thick coat sit on the rubber for awhile, then buff off with a terry. Let me know how that works.

Hope this helps...Lee