Got water coming down your back window? Wet headliner? It's not the rear window seal, unless the truck's been recently rolled over. It's that FED-Mandated THIRD BRAKE LAMP! This seems to be a common problem with the Colo/Canyo's. Drives owners crazy, some have even sued over it! Here's the problem. The seal is kinked out of place along the top, and clearly, it's been like that since install. Sparky (or Sparky's KID!) at GM was having a problem with the sticky stuff. You can see that the seal was placed, lifted (destroying the bond), and put back down in some ill-fated attempt to get it on straight. It's now UV-damaged, and the glue's long dried out. Carefully tear off the lifted old tape, back to where it's still adhering well. We can fix this, with some more of 3M's finest products. This is General Trim Adhesive. But don't try to spray it on the parts, put some in that old paint can cap there. Industrial-Grade Snot. Grab one of those Q-tips there, and... Wipe a liberal layer onto both the lamp body and the seal surface. Wait one minute, and then methodically place the seal where it belongs, taking care to do a better job than 'Ol Sparky Jr did. Doctored back up, it can be immediately re-installed. Leak fixed.