Ive discussed in other threads about my recently acquired 1991 Mercedes 350SD with the "rod bender" engine. The head gaskets are known to be weak due to insufficient material in some key places, due to the engine merely being a 3.0L block bored out.
The car had oil in the coolant, just the slightest amount, which could be literally absorbed out of the recovery bottle with a paper towel. But it would readily come back.
In theory, this means that retained coolant pressure would force hot coolant in the oil. In the few thousand miles I drove the car since buying it, it never lost coolant, and the cooling system worked well.
All the same, I pulled a UOA to see if there were signs of coolant in the oil. To my surprise there is not.
The soot % is surprising. I do think delvac 1300 has some sodium and potassium in it.