My wife's '94 855 Turbo wagon recently started leaking oil. It has 145k and never leaked before. Suddenly it's leaking/using 1/2 qt to 3/4 qt per 500 miles. The spot in the driveway got bigger until we took it to a mechanic. He said new valve cover gasket, then diagnosed the problem as oil cap gasket, which was allowing oil to leak under the plastic cover on top of the head. I thought this to be too good to be true. After replacing the oil cap gasket it is now pouring blue smoke out of the tailpipe but only at idle or low rpm. When at a vacuum it smokes like a two-cycle but after boost kicks in, smoking stops. He says new turbo...I think (hope) not. Could it be oil trap? What's causing high crank case pressure?

Thanks for the input!