First time it happened a few weeks ago I found the leak coming from the upper right corner of the trunk small seams(near the trunk hinge), so I put silicone on it to seal it but water is still coming in from another part somewhere near the antenna. it's dripping on top of the wheel well and from somewhere near the bottom of the antenna. I don't think it's from the actual antenna gasket since it looks like it has a good seal. I suspect it's coming from the bigger seam that runs from the bottom corner of the rear windshield to the trunk. Problem is I can't really put any silicone on it from the inside of the trunk since it's kind of awkward to to get to it with my fingers. By now I'm thinking of spraying some of that spray foam insulation on it,although I'm not sure if that stuff would stop a water leak. Anybody had this issue before? Thanks

 

Yup, I have this issue as well. It actually leaks on both sides. Have not found exactly where it leaks from. I would bet most, if not all XJ8/Rs leak water into the trunk; the owners just don't realize it because it's hidden by the carpeting. Who ever checks beneath all the carpeting?
Everyone should check under the carpeting and beneath the spare after a good rain or wash.

I discovered this when I removed everything out of the trunk to lighten the car for drag racing. I have not put back the carpeting since then, so the water can dry out when it does get wet.