Carbon seals are installed on the turbine shaft to control the oil flow when the throttle blades are closed. The vacuum draw is enough to draw oil into the intake pass the bearings.
Yep, that is one reason, MOST turbos available in salvage yards are not good for draw thru. They were used on blow thru, and don't have the proper seal. Some turbos do have a replacement seal set available that is compatable with draw thru.
I used a 1966 Corvair Spider (Rajay) turbo on my 65 Valiant 170 engine, back in 1979.
