Deep into it now!
Thermostat was there, and sitting in the closed position, but upon closer inspection and comparing it to the new one and the manual its not the correct one, AND the seal was missing/incorrect too... Result: Thermostat housing is corroded, and has a pin hole in the lower edge.
I cleaned it up and filled the hole and rebuilt the mounting flange with JB Weld steel mix. If this does not do it I will get a new housing.
Waiting for it to set now....

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2009 Mercedes ML320 Bluetec