oil in my coolant overflow

[benwadb1]

I have a jdm B20B in my db1 with the obd 0 everything wrapped around it an intake and full exauhst. Here is my issue the coolant overflow has been filling with engine oil, is this a head gasket issue or cracked cylinder wall? There isnt any oil in the rad, water in the oil, erratic idling, running hot any other symptoms and runs great any ideas?

[acb16a2si]

do a compression leak down test