The weatherstripping on my 69 convertible is in good shape (not crumbling) and obviously not 30+ years old. Is there a product that "renews" it, making it more supple? I've seen all the "shine" enhancers, but I suspect that they're only "skin deep".

Spray on silicone lubricant is supposed to help preserve weather stripping. Thats what I have always used. It seems to work well.

silicone dilectric grease works very well also, gm sells a small tube I could get part number if you want it

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My cars (http://www.geocities.com/gdwrench64/carphotopg1.html)

While it does work, I am not a fan of silicone. Raises he$$ in the paint shop. Have had good luck with some commercial rubber conditioners (silicone free). Stay away from Armorall, as it is loaded with silicone. If you never plan on doing any painting on car then it doesn't matter. Karl