I've actually had good luck with the JC Whitney "generic" window channel rubber. My experience has shown it to be of good quality, but I don't know for a fact that they have one suitable for a Merc in this case. I've used some in the past for other vehicles, one of which was still in good condition after ten years on a truck that sat outside its entire life. No complaints here with the window channel stuff they sell, especially since it seems to be good quality for a low price. Of course, that doesn't mean all their products are good.
