In my experience, that rubber trim isn't part of the water seal, so shrinkage is purely a cosmetic issue. But here's a company that carries pretty much any window part you want - including trim and seals. You may have to pull your trim out and take a photo of the end so they can match it.
Buddy Ray - Atlanta
Jayco Eagle HT 26.5RLS
Ford F150 Lariat, 3.5L V6 Ecoboost
Max Tow Pkg, 36gal tank
Reese Sidewinder and Reese Titan 16k hitch