If you found the oil in the tube between the airbox and the turbo i would be very surprised if the turbo was the culprit. More likely it is blowby oil collecting in there.The turbo at that point is taking air in and pushing it into the intake manifold if the cold side seal was leaking the oil should end up in the intake manifold.Try cleaning up the oil and relocate the tube from the valve cover to the air cleaner so it blows overboard temporarily.Be sure to plug the opening in the air intake so dirt does not get sucked in.Drive the car a while and see if oil shows up in the airbox to turbo again,my guess is that it will not,your turbo may be fine. Don
Red Green "This is only temporary,Unless it works!"
91 300d 2.5 250k + miles
87 300TD ?141k? miles