Some say the third brake light is the culprit on their trucks. You can test it with a garden hose. If your brake light is leaking you can buy some foam adhesive-backed weather stripping like you would use in your home, and place around the inside edge of your brake light to help seal it. I did this, but it didn’t help in my case.
My sliding back glass was manual but it leaked as well. After years of keeping the under seat bins full of oil dry, I got fed up and carried it to a glass place and had a solid rear glass put in. The guy told me he could fix my current glass to where it wouldn’t leak but at that point I was completely fed up with it. Never used the sliding part anyway. I’m not sure what he would have done to fix it but I would take it to a good auto glass shop.
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