Welcome to mercedes shop, one other place to check for oil leaks is the turbo drain tube. It has a rubber seal and o ring that goes in the top of the pan below the turbo. I have replaced them in both my cars. That was a big source of leaking.
Bill

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94 dodge cummings,86 ford 6.9,75 mbz 240d[ sold], 82 mbz 300sd,83 mbz 300sd