Just tried this method to fix an annoying rattle in my driver's door, and it seems to have worked perfectly. I found this product in the UK -
"Genuine BMW rubber care (spray)"
which I bought online at:
http://www.cotswoldstore.com/product...9_83120301480# (cost about £6).
It turns out that the can is labelled "Gummi Pflege" and the part number is 83.12.0.301.480.