I've been using Gummi Pfledge (bought from Detailers Domain, THANKS Phil!) on my X5, Audi and Toyota. The stuff is really great, and I feel like it's going to preserve the rubber as advertised. I wish I had known about it earlier with the Audi because I perhaps could have prevented a bit of deterioration on the door rubber. Highly recommended product!

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2003 BMW E53 4.4i Titansilber/Black
2008 BMW E90 328i manual
1972 BMW 2002 std Colorado Orange
2003 Audi TT 225 Coupe