need some help finding a leak

[AP Autosport]

I have a 89' 240sx with a sr20det in it, after buying this car I noticed a smell that didn't smell like the normal oil or coolent, but maybee a mix. Also, there is oil in the rad. overflow tank. The smell is not really there untill you are moving at a pretty good speed. I thought head gasket but I ran a comp. check and had even no. across the board and no spark plugs were fouled so I can rule out it leaking in to the combustion chamber. My next thought is the turbo, since its water cooled. My only problem is how can I tell, I don't want to replace it with another t-25 and I don't want to upgrade it untill I know there is not a problem somewhere else.

summary:1.sr20det motor2.oil in the coolent3.compression is fine and even, and no fouled plugs4.burning smell when in high gears at mid to high rpms5.I think it might be the turbo

[NISTECH]

loan a coolant pressure tester from autozone or some place like that. pressureize the system and see where it comes out