I've done two head gasket jobs on the M103. Do yourself a favor and have a machine shop machine the head and also replace the valve seals.

I bought my 300E post head gasket job and it still leaked because the shop that did it did not machine the head. You can do just the HG repair in about 15 hours for less than $500 with the head work. When I do it I replace the radiator, water pump, hoses, etc. etc. etc. though since everything is out and will have no chance of being contaminated with oil. This cost me closer to $1000 to do though.