I've heard that if you slit open the lowest point on the weather strp that it will resolve most of the leak, if not all. I'm not sure about it though.
On my car the leak was much more than a simple seal malfunction. The metal lip that the seal sat on was rusted and big portions of the lip were unsalvagable. I had to fabricate a whole new lip out of sheet metal. Then I rivited it on and used an epoxy called "Marine-tex" on it to seal it and hide the rivits. After that I grinded and sanded the marine-tex down and shaped it (like bondo). Then I rattle canned it... for now.
Marine-tex is the best epoxy that I've ever seen. It advertises on the box that it can be used to repair cracked engine blocks.
Here are some pics of what mine was like before.
In this one you can see my halfway fabricated new lip laying in the trunk.