Coolant leaves the engine by the oil filter, goes through the heater core then goes through the monovalve for flow control. Yes, the heater core can get hot when you don't want it to, such as when parked after a drive on a hot day. That's how MB made it.

Where is this EGR check valve? AFAIK there's a simple vacuum actuated valve on the forward exhaust manifold connector then a pipe to the intake manifold.

Sixto
98 E320s sedan and wagon