[Steve Tinker]

According to the experts, head gasket failure is rare on these engines. More likely is a failed heat exchanger or rubber O rings where the exchanger seats to the block. Oil usually gets into the coolant more often because of the higher oil pressure forcing it into the coolant.
I would remove the exchanger and have it pressure tested & replace if required (or turf it for a new larger S exchanger). New O rings are cheap.
Use the search function for heat exchanger and see the dozens of failures - you may be lucky and have a good engine cheap ......