I have a K&N air filter..... there is no oil in the air cleaner itself....... coming off the CDR in that hose there is a thin film of oil but nothing excessive.... from that point to the turbo there is also a thin film of oil but nothing excessive there either....... and obviously in the turbo you can see whats in there.....
Before you go condemning the turbo, go grab a paper filter element and stick it in the thing and see if that takes care of the excessive oil consumption.
I've seen this on a number of diesels that have put free flowing air filters on where they start inhaling oil.
The closed crankcase ventilation systems are designed for what little vacuum that there is on a diesel between the manifold and the filter , to create a negative pressure above the gasses and draw the blowby gasses from the crankcase off and burn them in the engine. When you install a free flowing air filter , you eliminate any restriction. Great for fast takeoffs...lousy for crankcase gas scavanging.
When a negative pressure does not exist to draw the crankcase gasses out, then they have to wait until there is enough pressure built up in the crankcase to overcome the pressure of the air in the box and be forced out. This leads to oil belching out of the breather tube.
I first ran into this years ago on a diesel car that I just HAD to have an open filter on the thing. I ended up having to rig an oil trap that I scavanged off of an Isuzu NPR at the big truck boneyerd onto the thing to return all the oil in the breather line back to the oil pan.
Racor makes a nifty aftermarket breather line oil trap for this purpose as well.
I just recently had to fool with a bunch of things and rebuilt my turbo just for giggles since I had the engine out for freeze plugs and had to buy a new pressure side impeller due to damage from too much dust damage and at the behest of the turbo shop ditched the K&N and stuck a paper filter in and low and behold ( and it didn't surprise me any ) the thing doesn't use any oil now, no more heavy dark streak in the filter housing