Turbo oil return line pressure?
 

What pressure do you think the oil return line on the turbo reaches on the highway?

Somewhere between oil pump pressure and crankcase pressure! Is this a test? Have you been playing with a pressure gauge?

There should be no pressure at all. Any back pressure or "head" at all can cause the seals to leak oil into the intake or exhaust.

The metal oil return line that was there stock was removed long before I owned he car and someone hose clamped rubber oil line to it. I'm wondering if on the highway it's spraying my turbo, intake manifold, and exhaust manifold from the increase in pressure. There's a layer of oil that builds up around there and comes back a few days later after I clean it off. Unless the turbo housing can crack and leak, it's the only thing I can think of.

Sounds like a leak or they used radiator hose and the oil is weeping through it. Most agricultural or truck places will have oil rated hose for sale.

Compare the ID of the supply pipe with the drain pipe. There's shouldn't be any worthwhile pressure in the drain pipe.

Sixto
87 300D