Leak Causing Rear Right Floorboard to fill with Water

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I have a 2002 Audi A6 3.0 Quattro with a frustrating problem! There is a leak in the car causing the rear right floorboard to fill with water. I had it into the dealer in Oct. 2010 where they replaced the rear right window chanels & seals & found the plenum drains & sunroof drainage to be ok, no blockage. I also had to replace the transmission module as it was filled with water from the leak! I have had problems with the rotation rate sensor & oxy sensor to the point of the ESP kicking on the anti-lock brakes at 60 mph, and have replace both of these sensors, thinking that was probably related to this leak also. I was vacumming out the car today and found the floorboard to be wet AGAIN! I’ve spent almost $6000 on my car in the past 6 months & have not one more penny. I’ve tried to get Audi of America’s help, only to be told the car is not covered under warranty & therefore there was no further help for me. The dealer just keeps the car for weeks trying to find this leak…HELP!

Did you buy the car new, or used? Could the car have been in an accident or flood?

The car was used, but checked CarFax history, no accidents or floods. The leak isn’t in the front floorboard either, just the rear Right side.