My door weatherstrips are showing their age, and I was looking for new ones on TFS, and of course they're discontinued by GM and they only have a few left, and passenger side only at that.
I've heard of weatherstrip restoring chemicals before, but suspected that they were just snake oil. I did some research and found out about a product called Gummi Pflege Stift, and read nothing but good reviews on its rejuvenating properties on seals and weatherstrips.
I've used it on a 98 bmw 528 to eliminate the whistling sound caused by the rubber contacting the window. I've also used it on my fiero door seals and trunk seals. Very good stuff, but a little pricey.
I prefer the spray ("tiefenpfleger") but Einszett makes an excellent product. I used Wurth's Rubber Care for many years but gave 1Z a try and haven't gone back. I use it on all my cars' rubber seals a few times a year and they continue to stay nice.
I use Gummi Pflege on my E46 M3. Good stuff. Doesn't last forever though. If you are trying to get rid of squeaks you need GM 3634770. VERY pricy but lasts a long time (years, or forever). It's a DuPont Krytox formulation. It lengthens the life of the seals too. http://www.ikvlubricants.co...k%20and%20Rattle.pdf