What is the oil pressure at idle/ half throttle/WOT?
The turbo sounds like the problem, could be backing up in the drain line or oil psi is to high and making it way pass the turbo seals. You can buy a cheap oil restrictor, might fix or help the problem. Not ever turbo needs one but it's good to have on older/used turbos IMO.
A rebuild shouldn't cost much, Blasstperformance.com(canada) does them for 150 I believe.
