Ditto to what Benzmac said. Also, although I'm not 100% sure if your car is the same as my 126, but there is a hose inside the tank flap, next to the fuel cap. On my 1983 300SD, this hose goes through the trunk and out under the rear axle area (roughly). If this hose comes off, like mine did, overflow from the fuel tank can get directly into the trunk area between the fuel door and the trunk hinges. I was able to push mine back on, but I had to climb in the trunk after removing the trim panel.

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Bob Roe
Lehigh Valley PA USA
1973 Olds 88, 1972 MB 280SE, 1978 Datsun 280Z, 1971 Ford T-Bird, 1972 Olds 88, 1983 Nissan Sentra, 1985 Sentra, 1973 230.6, 1990 Acura Integra, 1991 Volvo 940GLE wagon, 1983 300SD, 1984 300SD, 1995 Subaru Legacy L wagon, 2002 Mountaineer, 1991 300TE wagon, 2008 Murano, 2007 R320CDI 4Matic 52K, some Hyundai, 2008 BMW 535xi wagon, all gone... currently
2007 Honda Odyssey Touring, 2014 E350 4matic