recently bought a 1993 190e with the 2.3L engine. Went to change the coolant and it was brown like muddy water. flushed the system and put new coolant in. there is some residue in the overflow tank but no longer brown. I'm assuming I have a blown head gasket (or maybe had one in the past??) which is pushing oil into the coolant. I do not see any coolant in the oil. My question is when the engine is running the oil pressure should be higher than the coolant pressure therefore pushing oil into the coolant. When I shut the engine off and the oil pressure drops to zero wouldn't the coolant (which is still under pressure) migrate into the oil?

engine has excellent compression