From my experience, seals go bad from too much boost, too much heat, or too much oil pressure (or hitting them in the head with a club). You could check your turbo for shaft play and that could give you a guess if they are physically shot or not, but unless you were baking the turbo, or over-spinning it, chances are its just too much oil pressure, like they said.
You may also want to look at your oil drain. Make sure the drain in the pan is above the oil line. Oil comes out of the turbo frothed up, which makes it harder to push into oil, so if the drain is below the oil line, it could be backing up into the turbo.
–mark