Greetings.
I'm sure I'm not the only owner with this problem.
Whenever it rains or I take my G through the car wash, some water "pools" in the areas around the trunk weather seal. It's not getting into the trunk, but it bothered me. My theory was that leaf & dirt & crud was collecting and was "damming up" the drainage path, so I decided to take a look.
We CAREFULLY pried the "trunk finisher" panels off the sides, (there are small metal clips that attach to the round pegs) and sure enough, crud was to be found. I cleaned it all up and we trimmed the bottom edge of the finisher panel just a bit so the water could go where it was designed to go. Then we carefully reattached the panel (we had to replace the double sided tape at the front) by pressing down GENTLY where the clips attached to the pegs.
Click, click, click, DONE!
The whole job took about an hour. But BE CAREFUL!
AJ