1999 Contour passenger floor always wet underneath carpet, and soaks up to floor mats. Ive torn out as much as I can to see whats leaking and can find a moving drip but there are too many things in the way. Its been like this for years, ever since the dealership changed the cabin filter. Even took that out and checked around for a crack or leak but cant find one. Could the ac be leaking condensation down the firewall inside, thats where the water seems to be coming from. Also if the wiper washer bottle gets filled in a few days its empty and someone thinks thats the problem but i can follow the lines to the squirter and dont see any way that could leak into the inside. I just think the bottle may have a small leak, plus its in the front of the engine area far away from the inside.
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Homemade glass vaporizer

 

Had the same problem on my 98. I removed the black plastic trim piece at the bottom of the windshield (outside), which revealed an air intake duct. I took this off to find the seal was shot so I cauked it up pretty good and have been dry ever sence. Hope this helps.