Hard to tell, but if you've ruled out that head gasket as the problem, then there are only a couple more places that the oil can get into the cooling system. A crack in the block or head or the head gasket. A leak in the oil cooler. Or possibly a leak in the radiator between the trans cooler portion of the radiator and the coolant portion of the radiator.
It isn't uncommon for the deal/o-ring to fail on the oil coolers.
To confirm, so I'm not making you chase your tail, this is the diesel, cause I'm showing that the diesel is a 1.8L