I started a thread titled L series - Positive Crank Case Pressure, too much
http://forums.hybridz.org/showthread.php?t=121590&highlight=Positive+Crank+Case+Pressure read me!!
Here is what I have concluded with my L28 turbo..
when I am not running a PCV setup.. (ie open valve cover breather and open crank case breather) there is too much pressure in the crank case..
there is so much pressure, this stops the oil from draining out of the turbo into the pan. because of this, the oil backs out of the oil seals and burns in the exhaust!!
I ran the car for months without this issue.. but one day it just appeared. I fixed this problem by adding a PCV setup connected to the intake.
If you have a catch can, connect it to a vacuum source.
I have a strong strong strong feeling this is your problem.