I use the Lexol rubber and vinyl protector on all rubber and vinyl parts twice a year, seals, sun roof, trunk, under hood, around doors, etc. Wipe it on sparingly, not spray. It comes in the three part kit with Lexol leather cleaner and condioner.
There are a couple other brands that are also good. Just don't get a bunch of it on the paint.
Silicone grease might also be good. The spray doesn't seem to do much. I don't think I'd be using the lithium though, no good reason, but I think over time i will show stains.