Did you have the head checked for flatness to within.002", and was it checked for cracks? Did you clean the surfaces with an abrasive wheel to get the proper surface finish for the head gasket to bite into?
The next thing would be to use a cylinder leakage tester to determine which cylinder is causing the problem so you can look closer if things have to come apart again. The way you describe it suggests you won't even need that tool. To leak between an oil passage and a coolant passage through the head gasket is very uncommon.
The only other thing I can think of is some engines use an oil cooler that is a disc that sits under the oil filter. It's pretty common for those to corrode and leak the two fluids together on Ford trucks, but I don't recall your car uses one of those.
Thursday, January 28th, 2016 AT 5:30 PM