I Recently was looking under the rear seat to find a set of combination wrenches that I keep there. All of the felt liner was very damp and the wrenches were a bit rusty!!!

Does anyone know if there is a drain tube that could be plugged up or deteriorated that could be causing this ???

 

Betcha that you will discover that this is caused by a leaky third brake light.

 

There are drains on each side in the sliding track in my '06. They are hard to find. I had to remove the cables to clean mine a few years ago. Do a google search and you can find pics.