I have the same troubles. The gasket and pan seem to be tempermental on the reinstallation. The old pans lip was bent from overtightening so I was told. I bought a new pan and installe dit and new gasket. No leak afterwards for a few months, now leak is back. I think there is a trick to tightening the bolts ...not too little, not too much and the gasket and pan must sit just right. Seems hard to get it right without car on lift for a good look see what you are doing. My 190e 16v has sealed fine and leaked at the pan 3 different times. This last time even with a new gasket and pan. The second time the leak was there, the overtightend bolts had cut the gasket in two along one side of the pan. Definitely possible to overtighten and cause the leak. Be carful

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Christopher Henkel
1990 190E 2.6 - Arctic white SOLD
1986 190E-16v - Blauswartze
1993 300CE - SOLD
2003 W208 CLK 320 Cabriolet - Magma Red