If you have vents behind the rear windows.....thats the problem....just bang off the vent cover(it gets pushed on the sheetmetal rail and holds with its metal biting clip edge) with a block of wood and mallet that will expose the vent slots......then clean them well with a toothbrush and soap....let it dry well and smear clear silicone caulking over the cracks in the sealant that the factory smeared in there. What is happening is the roof drains down the sides of the roof and the water passes over the vent area....when there are cracks in the sealant the water leaks into the car through the rear roof post and drains onto the floor....usually by way of under the rear seat. Pull the seat and dry it all well after you fix the sealant leaks and you should be OK.