The trunk had been leaking water somehow for about 4 months. Finally had some time to take the lining out of the trunk to see if there was a rust hole or something causing a leak. To my surprise there was no rust or signs of a leak anywhere. So I left the trunk lining out and waited until the next time it rained, which was the next day (PA weather). Surely enough the water was leaking in between the taillight and the body. You need to remove the taillight. I sprayed undercoating between them. This solved the problem and the car no longer smells like wet sock!