if you raise the roof and the boot lid, so they are both pointing up to the sky , the point where the back of the roof has lifted to allow the rear panel to open, and stop it there, you can get access to the section where the hinges are easily. if you look down by the back of the rear quater window you will see a black rubber hollow seal, this is the one which the water goes down from the roof, also on the windscreen side you will see the same seal running from the top of the window down again to the scuttle, and along it various holes, just make seal these are clear
you tend to find at the bottom near the door the holes get blocked so the water doesn't drain..
If the rear glass has a small seperation from the cover to the glass in the corner, then water will get down inside the room compartment and either sit in the back near the rear lights or flow forward under the carpet and insulation and sit in the lowest point which just happens to be in the passenger foot well and houses the ECM for the windows, alarm, roof..etc etc... stupid design if you ask me!