Possible Sources of Coolant in Oil?

PRH said
On a BBM, it’s pretty much head gaskets or a crack/hole in a casting somewhere.

I assume the coolant level is dropping?

Not that I've noticed although it's basically been parked for 2 years so it's hard to tell for sure. It was just weird what when I pressurized the coolant system it held pressure - I would've expected that to push coolant somewhere.