restoring rubber around windows

[dads longhorn]

I have a 1971 longhorn unrestored and I'm cleaning it up. Part of the cleaning includes the rubber on the outside around the windows, gas fill cap, etc. The rubber is in great condition but has dry spots that are discolored, and keeps the rubber from being a nice plain black. I tried two things this weekend to clean it up 1) scraping off the discolored dry rubber w/ razor blade. works but leaves uneven color streaks. 2) bug and tar remover. petroleum based solvent, not sure it works too well.

So, I need suggestions on cleaning the rubber up. I think chemicals have the best potential. Thanks in advance for the help.