Originally Posted by
DmaxMaverick
Welcome aboard!
The first thought is, the exhaust system will hold a LOT of oil, and take a long time to clear. However, you are losing oil, so the problem still exists. The condition probably killed your original turbo.
That said, I'd start with eliminating the intake tract by checking the intake plumbing. A slight residue in the plumbing is normal, but if it's passing a lot (crankcase vent), it should be obvious. A head gasket failure or cracked piston will be seen as a lot of oil vapor huffing from the fill pipe. If it appears normal, get a close look at the turbo oil drain. Normally, it is zero/low pressure gravity drain. If it's blocked or restricted, in any way, by any means, a pressurized drain will force (a lot of) oil past the spindle seals.
While your other suspicions are possible, they are much less likely, as they are typically accompanied by easily noticeable additional symptoms.