Guy, stupid question, but have you tried this:
http://forums.quattroworld.com/a8/msgs/18945.phtml
I had water ingress problem in passenger footwell when I've just purchased the car. It was clogged rubber drain pipe which is easily accessible from the inside of wheel arch.
It can as well be gasket between electrical electrical box with all the control units and aluminium chasis of your car. Buy new gasket and change it preventively.
Here is example of what I'm talking about
:
http://www.passatworld.com/forums/68...en-filter.html