Gasket, 2pcs, A 199 077 02 79, about $2, available at Mercedes dealers.
Sometimes oil leaks there are because the insulating plate cracked or got deformed. In case you chose to have it at hand: A 129 074 01 81, ca $50 at Mercedes dealers. The availabilities and prices I am quoting are for Europe, but should not differ significantly in the US.
They are also available at, e.g. Authentic Classics.
May want to have a couple of, I think, 8mm copper sealing rings for oil line that may need to be disconnected.
I am not a mechanic, I did replacement of these gaskets myself, but I did it together with some other fixes around, so difficult to judge how much time it would take a professional to do just this. My guess would be closer to 6 hours or less.
I think it is indeed important to double check the FIP timing on assembly, just in case.