You're overlooking another potential source for oil at the turbo, and the most likely based on your list of problems. The inlet of the turbo connects to the engine breather tube. There's not much flowing through the breather under normal circumstances. But with a hole in the pan and/or leaky engine gaskets, the breather becomes another source of air for the turbo. Drawing air through the crankcase also means drawing oil.

The turbo produces only 1 bar of pressure at full scream. Nominal oil pressure is 3 bar according to the gauge, but probably peaks at close to 5. So if you were dependent on hydrostatic pressure to oppose leaks, you would have quite a mess. The shafts and seals are designed to float on a film of oil, which is why they may seem to be a loose fit.