Most likely your tail lights are leaking. The foam rubber gaskets tend to dry out and crack allowing water to run into your tirewell. You can take them out and use them as a pattern make new ones. I went to the local craft store and bought two 8"x 11" sheets of "Funny Fun Foam" glued them together with spray adhesive (to get the right thickness) used the old gaskets as a pattern to cut new ones, then siliconed them in. That fixed my tail light leak.
You can also get water in that area from cracked body sealer at the end of rain gutters on your roof. It can run down from there into the tirewell causing the infamous hatch strut leak. Carefully inspect the body sealer at the end of the rain gutters for even the smallest cracks. You can seal these with silicone or seam sealer.
You can also get water in that area from cracked body sealer at the end of rain gutters on your roof. It can run down from there into the tirewell causing the infamous hatch strut leak. Carefully inspect the body sealer at the end of the rain gutters for even the smallest cracks. You can seal these with silicone or seam sealer.