I have the same gasket and it is going back!
I had issues with the rubber I got from Chevs as well. The back glass rubber was destroyed trying to make it fit & the vent window seals were a joke. They were an inch too short. Try driving with a half inch gap at the top & bottom of the vent window in the rain while listening to the whistle. I don't know who made the back glass rubber but Metro Molding made the vent window seals. I bought replacements for both from Steele & they fit like a glove.
