rear window leaking

My rear window near the passenger side post started leaking again (see previous post). This time I researched before calling my local service department. The problem is either 2 things. 1) the 3rd brake light housing gasket has failed 2) the seal around the rear window has failed.

I did a test. I turned the truck on and turned the air to full. I closed all windows and doors. Waited 5 mins. I took a spray bottle filled with dish soap and water and sprayed the window corners and brake light. Observed. No bubbles at the brake light, but some large bubbles were quickly being filled at the passenger corner. Clearly, if a little bit of air can breach the seal from the inside of the cab, water from the outside can get in. I'm almost (can't say 100%) certain this is where the leak is from.

I tell Ford my findings. They want to run their own tests. The results come back positive ... I have a leak .... from the 3rd brake light. What? I'm already on my 2nd brake light assembly. I let them replace it since it's free, but am left feeling like nothing was accomplished. Now I have had 3 different brake lights on this truck.

Fast forward 3 weeks. Water is found leaking from the same location after the first legitimate rainstorm since the brake light fix. I called Ford service, they want to run their test on the 3rd brake light. I tell them that's not the problem.

Looking for a DIY fix on my window seal ....