I'd have to say that the owner of the truck is most likely wrong. It probably leaks while the engine's running and has oil pressure. He notices it after the engine's shut off. Although it is possible that the seal between the oil pan and the rear engine cover isn't very good and when the engine's shut off, the oil drains back into the pan and the oil level rises. When full, I believe that the level is higher than this spot. That's the only way that I can see for this spot to ONLY leak after being shut off. Does the turbo make it harder to work on these things? Yes, for some things like injectors, glow plugs, maybe the valve covers. Don't let that turn you off though. When everything's working right, the turbo makes it a different truck entirely. By doing a few modifications, you can make a Factory Turbo perform the way that it should, not the way Ford released it.