oil in the coolant

your best choice is a head gasket made by Victor Reinz, which is the same company that makes them for MB. there are no ongoing problems with the 103 engine if the head gasket is installed correctly. the "musts" are as follows: the head bolts must be replaced (they are stretch bolts), the heads must be resurfaced or at least checked for flatness at a machine shop and whatever caused the engine to overheat in the first place must be fixed. this means that you carefully need to check the radiator, the auxiliary fan and the fan clutch---literally, all the items required to keep the engine cool. and always, if the temp gauge begins to climb while stuck in traffic or when driving, you must head to the curb immediately. my shop has NEVER had to go back into one of these engines, so there must be something that you've overlooked.