The roof rail weatherstrip starts at the door edge were the chrome boomerang also mounts. The roof rail weatherstrip has a metal strip with two threaded studs that are incorporated into the strip. The section of weather strip runs the entire length of the roof rail down to the near bottom of the door jamb. Perhaps the part you are talking about is the square shaped metal coated rubber piece that goes in the door jamb and covers the quarter windows base mounting? NPD has this part...pillar mounts I believe they are called.Hope this helps..I just installed all these parts less then a week ago myself.