Hahahahahahahaha! I finally beat the leak(s) after many months of troubleshooting. I had a leak in not one, but 3 different locations, all on the passenger side. First was the aforementioned vent. Pulled the gasket out and put silicone everywhere...still had water in the trunk, but not from the vent. Second place I found was around the non-power antenna housing on the outside of the car. The plug/connector at the end of the antenna wire was rusted because water had come in there. A little silicone around the outside rubber housing fixed that leak, but water was still getting in. The last and final place I found it leaking was through the passenger side trunk arm hole(for lack of a better name). After I removed the rear shelf I discovered it was coming through the backglass, missing the shelf material(there is a recess in the corner) and dripping into the trunk BIG TIME. I peeled the rubber moulding from around the leaking side and added a bit of silicone in the area I thought was to blame(using a hose to see where water was possibly entering). No more problems(knocking on wood...lol). My advice is to pull all the carpeted pieces out of the trunk, get a flashlight and a towel, and have someone use a hose from outside to trickle water down the backglass. Good luck to you, I know it is very annoying! The water warped my sub box, giving me reason to build another.
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