Gummi Phlege is available through all BMW auto and motorcycle dealers. If they don't have it on the shelf then they can order it. I can't remember the cost. Nothing extroidinary. One aerosol can has lasted me at least two years.
It is a very thin, clear substance that I spray into a rag or applicator and then wipe on the soft seals. It doesn't coat them as much as it seems to "absorb into" the seals. It makes them "blacker" and very uniform in color but doesn't leave any type of fake shine that will wear off. You can feel and see the difference immediately and for several weeks after application. Hard to explain but the difference is amazing.
I have used it on my cars for years now and haven't found anything better for soft seals.
I think, roughly translated, Gummi Phlege means simply, Rubber Care. Clever Germans.