Oil operating temperature is perhaps sub standard on these engines while operating? Has to reach at least 250 degrees to clear the oil. If these engines have oil coolers they are too efficient or the thermostat to put the cooler on line has a wrong value or is non existant. Oil does not boil till about 600 degrees if I remember.
Mercedes could have cheated on design and are trying to remove too much heat from the oil. Really hot oil is probably not a good thing but neither is oil running too cool. The gentleman running 40 miles each way does raise this as a possibility in my mind. I would contact mercedes and talk to them. Almost indicates this engine should not have an oil cooler if it has. I do not know anything about this engine I freely confess.
Also if crankcase ventalation is that tight and it is really the problem it should be modified to preform it's function. A straight road tube modification would be vastly superior in my mind.
Sounds like perhaps some poor design issues here. What is baffling is this area of engine design is so old how could they mess up this bad? A very junior engine engineer would catch it in the engines development stage. Does this company no longer care?