The OM617 Turbo builds "pressure" inside the intake manifold = bad valve guides and/or seals allow additional pressure into the valve cover/crankcase.

OM617 blows exhaust gasses/plasma "pressure" out to spin the turbo up to speed = higher pressure in the exhaust manifold will seek any escape = bad valve guides and/or seals allow additional pressure into the valve cover/crankcase.

Note:
I had a demonstration head from an OM617 at the January 26, 08 Cold weather Diesel Tech Session ++ Detroit event.
The best valve guide in the cylinder head showed 0.11429 MM slop, can't find the spec at this moment, however that is way beyond junk.

If a valve can be moved sideways in the guide at all, that guide is junk.....

On a turbo you go from neutral to a lot of positive pressure in the manifold. With the rocker cover off, you can manually rev it up to create boost pressure, and sometimes see oil blowing up away from the valve seals = positive proof of a bad valve guide.