Hey

Are you sure that isn't automatic transmission fluid? Is the engine oil really going low?

That would have to be a pretty major leak in the head or head gasket. You might try pressurizing the cooling system to check if you can hear coolant running somewhere into the oil. I don't know how effective this would be for this problem, but if you can find a smoke machine to borrow, you could use that to pressurize the cooling system or the oiling system, then try to see where the smoke is sneaking out.

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.