I do not have an easy answer for this one, of all the people I have spoken with; we've concluded it was a combination of things: an air pocket in the casing process combined with heat (egr blocked at intake manifold) and corrosion. Once this took its toll on the pocket and it finally opened up enough, this allowed the exhaust gasses to get around the gasket which caused me to hold higher temps and push coolant.
Even though the car never overheated (or mixed fluids) and in my opinion a healthy set-up does not push coolant, I would push a table spoon worth of coolant after a couple of 5th gear pulls. This was verified by me using white shop towels next to the overflow tank. I then put the car away in the fall of 09 and bought a ported & built head knowing this one was coming off. All of my testing pointed at one thing, a bhg very, very early in the process. The head was pulled off the motor in the fall of 10 and once I started my clean-up & sell off I took the head to the machine shop to see what it needed. Since the only issue was that around #6, I decide to have the machine shop fix it and it is now up for sale.
Let me know if you have any more questions and or need more pics.