K24 Turbo Cold Side Seal Question

[Fred Munro]

I have a question for those who have taken apart a K24 turbo.

What kind of seal is used on the cold side shaft to hold boost pressure?
Ceramic, dynamic, labyrinth? Does it need oil pressure behind it to seal
properly?
Reason for the question:

I was testing the intake system on the S4 for pressure leaks yesterday. Had
the hoses off at the throttle body and ISV and plugged. Had the hose off the
crankcase vent on the cam cover and plugged. Pulled the hose off the mass
meter and pressurized through it. The system was losing pressure and I
noticed a typical PVC smell and a small flow of air coming out of the cam
cover crankcase vent.
The only thing I can figure is the air was getting past the cold side seal,
down the oil return line, and into the crankcase.
Car doesn't use or burn oil, so it doesn't seem oil is getting past the seal
into the intake. Anyone know what this seal looks like? Should it hold 20
psig pressure on it's own?

TIA

Fred Munro
'94 S4