Based on the location of your leak, I'm betting it's your rear moonroof drain - plugged up or disconnected.
I'd park the car with the tail slightly low, and pour a cup or two of water in the channel of the open moonroof, and see if it immediately runs out somewhere behind the rear tire. If not, you found your problem.
I'm betting you can see the bottom of the drain tube when you pop out the rear side panel on the left (assuming that's where it's leaking). It could also be clogged up by debris in the inlet to the drain tube, back by the rear of the moonroof channel. See the diagram below to get an idea how this all works: