I recently pulled the carpet from my 240 passenger and driver side. I had a leak from both sides up at the top of the dash. You could see small rust spots in the seams at the top of the dash (firewall?). Anyway the carpet was wet and the metal plate the wires go under was totally rusted. I also noticed some spots where bubbling of the undercoating on the car in these areas and under the drivers seat. Was this caused by my inside leak or from the bottom of the car?. I really want to correct the problem before I lose the floor. How long would that take? I sealed and coated the firewall seams inside and out using rubberised paint. I also painted those lower sills inside the car where the water seems to sit.