The water test ought to be conclusive.
Find leaks is listed as one of my hobbies as it always happens to me in all the cars I had. Perhaps I have this affinity to attract water as I do trouble?
Well, the likely place to start would be to open the trunk lid, and start flowing a steady amount of water through the rubber seals. A waering can would be ideal if the garden hose is too far away. Not to strong water that would splash everywhere and confuse the whole test.
You may also flow the water from the top but I doubt if water leaks from the top of the back w/screen ranks high in probabilities.
Observe any build up of water in the trunk area. They start as small traces which would then accumalte and form a small but significant pool. At which time you would know by now the flow of water and how it enters the prohibited area.
You may also want to do the same on both tail lights as the tail lights has:
1. those plastic lenses which may allow water in too;
2. weak rubber seals and gaskets;
3. a slight crack somewhere either in the rubber seal or len which would allow water to penentrate.
Let us know how much water used ...
