Ideas others have used for the Retun Oil from a bypass Oil Filter.

Drilled and tap the Valve Cover as ForcedInduction did in post #30

Amsoil I believe sells Oil Fill Caps that have the return fitting on the cap. However, I do not think they make one specific for Mercedes.

When I fist did mine I removed the Dipstick and had the return Oil going down the Dipstick Tube. It worked and required no drilling but was a pain to check the Oil becaue I had to remove the Hose attachment to insert the Dipstick.
So I relocated the return as in Post #70

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84 300D, 82 Volvo 244Gl Diesel