Originally Posted by 70GT6

Another source for the leak can be the rear wing.
There are small o-rings that if torn or out of position will cause a leak.
If they leak, water will follow the plastic trim and drip in to the rear well.
I removed my rear wing cleaned the area and used silicone gasket maker instead of the o-rings to seal the wing bolts.
Worth a look. You will know if they been leaking because the area will be a bit rusty.