This weekend I solved the water leak in my trunk. It was such a simple solution too. Every time it rains or I wash my car (which is weekly) I get water in my trunk. It has been raining in Raleigh ever since I have been here in the beginning of May weekly. The water builds up on the passenger side. I removed the plastic cover on the side, there was about 2 inches of standing water. I then saw the rainbow clouds of oil or gasoline sitting on top of the water. After taking off the metal plate in front of the fuel tank I discovered the problem. Under the fuel filler flap is a drain hole for over pumping of diesel. This hole is connected to a rubber pipe to drain the diesel off under the car. The rubber pipe was disconnected, and all of the water was draining to the trunk. I hope that this will help other in their search for water leaks in the w123.

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1983 240D Yellow
1989 300E Champigne
1993 190E Gray
1986 325 BMW Burgundy
1987 Chevy S10 Blazer