Many people think that the rear trunk seal is failing when they get water in their rear trunk.
In actuality, the rear tail lamp assemblies are leaking. In order to solve this problem, you need to remove the rear assemblies and then replace them with some caulking material. Not being a great fan of the black silicone caulk that messes up everything unless applied by Michaelangelo, I decided to use some caulking that was pre dispensed into a roll. I bought a roll of this at Home Depot, and simply applied it to the rear seams of the trunk before I put the tail lamp assemblies back. This is important, because the trunk is a favorite spot for rust to appear.