"If the turbo intake is relatively clean, but oily goo is coming out of the compressor outlet and ending up in the intercooler, this can be a problem. Given enough time, the goo effectively blocks much of the core, starving the engine of air."
I assume the compressor needs a rebuild or replacement if this is the case?
Well, that depends. All of the 2005-2010 model year truck have turbos that seem to pass some oil to a degree.
If the turbo has no perceptible axial play, and not enough radial play to touch the compressor wheel against the housing at all, and it freely spins and doesn't stick with some pressure put sideways on the shaft (this is hard to describe), and what its leaking is oily and not like tar, then its probably ok.
If the hose from the turbo to the intercooler has sticky tar-like junk building up in it, or if oil has made it all the way through the intercooler into the intake manifold, then you have a problem.
Its very important to make sure that any excess oil is not coming from the crankcase breather. It enters at the turbo inlet. If you only look at the turbo outlet, you only get half the picture. Being overfilled with oil is the main cause. These only hold 16 quarts of oil, more does not help. This is a frequent, easily preventable problem.
If the engine has high mileage and some blowby, the crankcase breather cap and coalescing filter from an 11-13 truck can be added. There's a piece inside that will have to be removed for the filter to fit. It just slides out. The filter change interval is every 60k. It helps with condensing oil vapor back into a liquid and returning it to the crankcase.