Although, it is possible for the head gasket to leak after a refresh, it is rare. I have heard of cheaper Victor Reinz head gaskets failing short after, but if this is a MB gasket bought from the dealer it is the updated style with reinforced steel which makes it more unlikely and probably the u-shaped gasket giving it that leak you have now. Personally, if I were you in your shoes I would do ALL the gaskets now that are relevant when you go to fix this oil leak. Timing cover gasket, valve cover gasket etc just to get it out of the way for the future.

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k