There are a couple areas that typically leak. You fixed one, being the tail lights. Another problem area is usually the sunroof drainage tubes. These run from the sunroof, down the rear pillars, and out the rear quarters. A good idea, if you really want to find this leak without checking everything, is to remove the interior from your trunk (carpeting), and spray sections of the rear with a garden hose. Do one area at a time, and check the inside to see if water got in. This will help you pinpoint the problem.
I had a leak in my trunk, and did some investigating. It turned out there was a crack near my driver side tailight. When water ran down the roof, and along the trunk cavity, it ran down the taillights and into the crack.
Good luck finding it. The water in my trunk actually sloched up and got my rear seats soaked :lame:
