[john]

Whoa, that is a lot of oil. One quart per tank of gas. I think you have the most likely causes down. Could be something like a seal on the front case or something... I would definitly do a compression test now. See where you are at. The numbers will be low if the valve seals are leaking or if the rings are shot. Feel the turbo next time you see it. See if it smokes after reving it. Rev the car at the throttle body to ~2500 rpm and check for smoke at the turbo.