Your tech missed on this one. The condition he described exists on many cars but not your MB. MB limits the amount of crankcase scavenging to what can pass through a metered oriface. The amount is considerably more than that which a good engine gives off in blow-by. Because the volume through the oriface is always greater than blow-by a significant vacuum would occur in such a situation. MB balances this by allowing air to flow into the valve cover from the air cleaner. Thus total air flow is blow-by plus intake air at V/C. There is no pressure differential.
BMW, Porsche, some models of Volvo have systems like your tech described but not any of the variety of K-Jet systems used by MB.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician