How do I stop leaks?
From Phil Bush:
In the tail lights?
RTV was suggested to stop taillights from leaking. I went and bought a replacement gasket (about 8 bucks) and resealed it myself. It leaked a little after that, but now does not leak.
In the trunk?
Part of the trunk leak problem is the water actually leaks around the tail light assembly. The water runs down the trunk lip channel and drains right across the tail light. The seal between the light assembly and the car is some foam job that is not adequate. Use bath tub seal around the top 3/4 of the light.
Another part of the problem is if you park facing down hill, the water puddles in the trunk lip channel at the forward edge of the trunk. The rubber seal deteriorates by not contacting the trunk, cracking in the middle and lifting from the seal support. To repair, remove the seal and apply black silicone in the vee and put it back on.
You may also find water in the spare tire well of the trunk. There is an oblong access hole in the sheet metal underneath the tire well. This is sealed with a metal insert, but the joint is not watertight. Apply a bead of silicone around the access hole, and voila! no more leak.
Underneath the floormat
There is an oblong access hole in the floor pan underneath the rear passenger footwell, just like the one in the trunk. Smear silicone around that as well, and no more leak.
From the moonroof
Thanks to Gene Fornaro: After verifying that the four drain holes were not clogged (open moonroof, pour 1/2 cup water onto track area; should drain out holes - one in each corner), I hypothesized problem was water wicking through the felt/rubber seal. In other words water actually adheres by surface tension to the seal and migrates toward the inside of the car without dropping into the drain track area. My first fix attempt involves painting the seal with silicone water repellent. So far, so good. Water beads at the seal rather than trying to soak through. Interior dry through three rain storms.
Silicone waterproofing is available at shoe repair stores. Find one with a small brush or dobber for application to the seal.