Remove the Cowl vent panel under the wipers. Each corner in the basin has a square drainage hole. Make sure they are clear with a blower or long wire. They get clogged with leaves and debris. Test it by pouring water and see if it drains under the fender. Drill additional drain holes if you want, at the bottom of this metal basin. On the back of this basin you will see a large rectangular hole where the air is sucked in for the heater. That is where the water gets into if the drainage is clogged. It then shoots through the vent under the drivers seat, aiming to the rear. that is why you get a wet rear floor.
ari, December 2011