It could be a leaky rear window seal combined with how you were parked at the time of the massive rain storm. It has been raining here in Kentucky a lot too. Yesterday, I noticed where the water was getting into the trunk of my '83 300SD.

Just an idea.

__________________
1983 300SD - OLLIE
1985 300D-HILDA (SOLD)
2002 VW Jetta TDI - Puddles
____________________
Diesel passt mir leid!