I'll add to the recommendation for Nextzett Gummi Pflege. Not too expensive (especially for a German product) and readily available via Amazon.
It's the closest thing I've come across to the beloved old BMW Gummi Pflege ("Rubber Care") gel that came in a tube. The applicator sucks though, so just wet a towel and apply it that way.
The thing about these two products is that they don't act like greases; the carrier evaporates and leaves a slick, softened surface that won't stain windows if given enough time to dry. If not glyercine-based, it certain acts like it (slick and hygroscopic).
I'd save my Syl-Glide for my brakes, even if it didn't gum up after time.