Are you sure u really searched? Cause i recall this topic being covered multiple times.
Giving you the benifit of the doubt, there are many many many many many places where you can get your car checked, serviced, etc.
Hyperdrive, cypher, evolution r, top racing, speeworks, etc etc etc.
Having oil on your turbo is never a good thing, it usually says your turbo is in need of a rebuild or a new turbo is in order. That'll set you back by a few grand for sure.
Don't you have friends that drive STIs and stuff? I'm sure they do service their cars, modify it, and stuff, they'd know good places to go to wouldn't they? The GTR is an awsome car, but is not that complex/complicated. Not as complicated as say, a porsche 911 turbo. So most performance shops would be able to do the necessary stuff for you.