Just thought I'd post this up for what I did to solve my problem of the 3rd brake light leaking. I was getting water in both rear top corners of the cab where the headliner meets the plasic and rear window glass. What happens is the water leaks through the seal of the light, then makes it's way into the cab sheet metal, and runs to both corners due to the way the metal slopes. If you have water dripping from the top corners of the rear of the cab it is probably the 3rd brake light seal leaking. First thing I did was check to make sure the window seal also was not leaking, by pouring water in the open channel (once you remove the two screws holding on the light and pull the light off). There are weeps that let the water drain at the bottom of each corner of the window, my passenger side weep is wide open, the driver side weep is a little tighter (due to the window being installed slightly crooked), but it lets the water out fine. So anyway I then cleaned the sand/muck off where the light seals, and cleaned the old gasket off the light (very easy with flathead screwdriver, then again with adhesive remover). I then applied new thicker gasket (not a foam type like the original), I bought it at home depot, it is slightly wider, and about twice as think, but still very compressible. This is more rubber like (EPDM) than foam like, so should seal better. It doesn't turn sharp corners well, so I cut about half way through for the top two bends, and cut a separate strip for the bottom, this way the bottom corners are open and will let any water that may get in drain out. Pics....