Sounds like you have it covered. Probably your area with most leakage is the turbo oil return - especially at the pan end. This is pretty typical. There is also a big ol o-ring at each end. It sounds like you may even have a slight leak in the line itself OR the tube from the bottom of the air cleaner to the oil pan. I have seen some rub marks on these - especially where the bracket has broken loose from the support underneath the turbo.

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Jim