Another location to inspect for water leaks is the corrugated rubber connector that covers the vac lines and electrical wires going into the four side doors. I am sure that the one on the front passenger door has caused my front floor wetness. Also the way the car is parked can change the location of the pooled water, ours is always parked at home with the nose pointed down hill and there has never been a drop in the back footwells.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150