Mate i have a 2002 WRX.
I split a hose on the turbo and replaced it before I knew about the inline olive.
5PSI was all it would boos to.

I now have a manual boost controller and were back up to 15psi.

The O2 sensor is gone and it made no difference, I just put a resistor in the plug after a couple of months so the light would go out.

I would say it's had a manual controler and th hose with the olive in it has been "lost"

if you can get one and replace it I reckon your on your way. otherwise get a manual controller and set it at what you want... I have done track days andd use as a daily and my car is till pulling as strong as it can with a td04 and stock tune.

However I agree with the other guys.... get a good mechanic to go over it, OR wait till exactly what you want comes up.

hey you can buy mine if you want...