NWS6

As you chase down the cause of your leak, don't forget the fresh air intake gasket previously mentioned. This might be the most common source of C5 front passenger foot area leaking.

It's hard to see the problem until you take it apart. I did mine when the windshield was being replaced. The trim being off made it much easier. Note the bolt hole locations, that back one is troublesome. Here's some photos that may help.

Doug Leach

i believe I'm up against the same problem of the cabin filter gasket. Why in the world am I even going to replace this thing? How about a bypass & block this hole directly into my car and floor...AND TCM ! What a crappy design...along with only a piece of plastic to shield it? i want to relocate the TCM, silicone the windshield plenium and lose the cabin vent concept completely...
Anyone have a better design?? Maybe relocate the battery while were at it to the trunk
Much appreciated for any ideas!!

georgeb944

Yep, it's a terrible design. Either fix it or sell the car.

Harleyguy

One possible solution: 1) Go to your local hardware store. 2) They usually have styrofoam filler rod for sale in various diameters. 3) Buy a size that matches the old gasket material. 4) Clean out the old material from the groove. 5) Apply the filler rod to the channel you just cleaned out and attach the rod material using weather strip cement. Cutting off fresh air supply to the cabin is probably a really bad idea. It will not allow for an air exchange that among other things helps to dissipate condensation and CO2. Or like george said, get rid of the car.

Keheuer

​​​​ The easiest way to tell where the water's coming in is to feel the cabin air filter. There is no cover on the cabin air filter for an A6 wagon or an allroad. If there is water on the cabin air filter after you hose your windshield, it is not the gasket for the cabin air filter box.
I have had the same problem as multiple other people. A poor windshield replacement does not allow the cowling at the bottom of the windshield to snap into place properly. I just had a crack in my windshield and I'm getting it replaced on Tuesday. I will be on hand to make sure they put it in the right place and the cowling is properly seated. It seats and snaps in place flush in the middle of the windshield between the windshield wipers but on the sides it doesn't snap completely in. I don't know if it's because it's old or because it wasn't installed properly but that is the cause.