I seem to remember the u-shaped plastic being in some vents, can't remember what year, make model anymore. When we were replacing vents and doors on these trucks on a daily basis we used either cork/rubber or rubber setting tape. We had several different thickness's of both, just found the one that worked best. You would probably need to find an older glass shop that has a supply of these, they should be able to fix you up. The oil on the rubber tape will soften and lubricate it easing installation. Heating the tape with a heat gun or torch gently will also help. John
