I bought a "brand new" turbo a few years ago and had the same problem, replaced the head gasket twice, drove myself crazy for a week. Turns out the center section of the turbo had a crack in the waterway causing it to allow coolant to get into the oil. The way I found this out was to dissconnect the water lines to the turbo and run the car for a few minutes. I hope this is your problem and not a cracked block/head.

Let us know.