this is more of a general interest following a conversation i had with Ste about oil seals on turbo's. This is taken from "Rolls Royces The Jet Engine book" but is still aplicable to this application. Most of them rely on an abradable lining with a metal ring that cuts into it, air pressure on one side holds the oil back in the bearing chamber and back out on its return to the sump.
(http://www.stuandele.co.uk/mr2roc/seals.JPG)