I had a lake in the backseat passenger footwell area...after checking around, I found the right side cowl drain (under the battery tray) was completed clogged up with flaky-leftovers of what was once my battery tray. the water was building up under the battery and then seeping into the car through the rubber grommets in the firewall. These cowl drains empty into the wheel wells...look for the grayish-black plastic drains, visibel from the wheel wells. Both of mine (left and right) were pretty well full of years of New Mexico sediment/mud. clearning those out (accessed from the wheel wells) helped the draining immensely (the right side drain gave off an interesting collection of red N.M mud and rust flakes from the aove mentioned battery tray. Anyhow, not more problems with water inside the car!

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1983 300D 218K miles