This can be tricky…when you first had the head gasket done I am assuming it was because of either your oil was milky or visa versa…now after you changed everything and properly fixed the head…Did you ever pull the radiator and run degreaser thru it? Oil is a ROYAL BITCH to get out of a radiator…perhaps you have residual oil contamination in the rad that was never removed after the first failure. That is more likely than a failed repair attempt I think… Unless you wrecked your engine block…then it can mix it up at that point… Your radiator can also have a cracked trans cooling line…if that line fails then you will get oil intermixing in the rad as well. Is your engine oil milky too? If your hoses and rad were not properly flushed out with hot water and a mild degreaser I would have done that.
What was your inital failure?