As a rule of thumb it requires oil pressure to get that much oil into the
coolant and those coolers go bad all the time.

As for coolant in the oil you would have to have more pressure in the cooling
system then the psi of oil pressure which could happen after you shut down
the motor but this does not sound like a good sign.

The first thing to do is replace the cooler (and change the oil) and then
what I do is pull hoses and get as much of the baby shit out of the system
with a hose, reconnect hoses dump in a cup of dish washer detergent (It does
not foam) let the thing run for a while and then flush it again. This is the
quickest way I have found to get all that oil out of the cooling system.

pressure test cooling system to check for coolant leaking into the oil after
replacing the oil cooler.

Jeff E.   Lilburn, Ga.
87'WESTY Weekender (BOXOBLOX)
87'GL