It could also be the mitsu compressor bypass valve...it's more like a blowoff valve and it dumps compressed air (and any oil) onto the bits near it. It opens every time you lift and the turbo is boosting. If it's faulty it blows while you're boosting.

Another test for turbo'd cars is after you've thoroughly warmed them up (and whassup with such a short test drive that you have problems 10miles down the road after buying it??) and done all your performance tests, let the sucker sit and idle for 5-10 minutes. If it smokes like the Marlboro Man, adjust the price downward about $1200 for a turbo replacment (although I just replaced my stock Mitsu on a 90 740T for under $500 and some knuckle skin...).