I got into similar situation last weekend after 2 hours of heavy rain. Dont know what happened but I had a pool of water on the passenger side rear compartment with load of its underneath the battery tray. The fabric was wet from the compartment to the trunk floor arear.

I already soaked out the water but couldnt find the actual reason. Possibly sunroof but also the plasttric trim next to the taillight. Icould see it cracking and leaves a gap there but Im not sure. Any body has the part number for those 2 plastic pieces?i looked up on realoem but couldnt find