SO After Extensive water testing for about 3 hours this morning. Its not the 3rd brake light nor is it the rear window seal from what im experiencing .
After digging around every inch of the driver side corner , I have found the weather stripping on top the roof to be warped and not seated properly.
I blasted the roof seem from front to back with the truck on a slope, and i get tiny beads of water, in the same corner.
My 3rd brake light was absolutely dry on the inside, Aswell as my Shark Fin Antenna this AM after a night of rain .
Here are some picture i have taken, maby this is your culprit Aswell.
one is the driver side (leak)
other is the Passenger side.
You can clearly see the molding trim not flush to the edge of the seam.
Also looks like either the Molding is to small on the driver side or the Actual Frame it self is wider in that spot , because you can clearly see the difference in the gaps.