I used to use some dry silicon thingy on my e46, no problems with my e90 the last 5 years (so I don't recall what I used to use) I did a google search and found something promising.
http://www.z3bimmer.com/OffTopic/E24Bimmer/Gummi/
I'm wondering if this, by conditioning the rubber also acts as a lubricant too.