All,
I have used Gummi Pflege on my 2001 525i rubber around all the glass. It definitely helps keep the rubber soft, possibly too soft.
I happened to see a bug splat on the rubber that is around the windshield. So I proceeded to remove it using my finger as I do on the paint. My finger nail sank into the rubber and left a small in the rubber. I was amazed how soft the rubber got after two applications of Gummi Pflege within a 1 week span.

So, yes Gummi Pflege makes the rubber pliable and keeps it from splitting, but watch out. Don't apply any pressure to it when you clean the rubber. Use a small damp sponge dipped in a bug cleaner and massage lightly.
I have learned my lesson on this the hard way. So please learn WHAT NOT TO DO from my experience.
crisslo