So I was concerned that the door seals on my X5 were deteriorating as I've noticed a bit of road noise recently. I search around and found that most BMWheads use a produce called Gummi Pflege, which was once made by BMW (is not anymore) and now has several knockoffs. I used 1Z's version, which is made in Germany and I believe water-based. Here is the link:
Einszett Rubber Care Stick Gummi Pflege, gummi pflege
In short, am very happy with the results. The seals are definitely softer and blacker (similar to new seal color), and it's probably in my head but I feel like my X5 is quieter as well. I highly recommend it for $9 if you plan on keeping your X5 a long time.
-Cyrus