I did use Gummi Pflege to try solving this myself. It did reduce but not eliminate the problem. The dealer service manager cautioned me against using non BMW approved treatment on the seals as it could void warranty which led to a heated discussion.
The first attempt of the dealer was to treat the felt seals ... This seemed to fix the problem for a whole 100km. So far the second fix from the dealer - Teflon tape seems to be working.
Your fix is interesting as it gives a more complete picture of the cause whereas all information to date seems to implicate seals, felt etc as individual considerations.
At the end of the day....I should not have to treat the seals every few weeks. There is either a design flaw or a batch issue with seals as it is reported by others. This needs to be ddressed