Originally Posted by Maxbumpo

Let me correct that: Minimal oil will flow down the stem/guide to keep it lubricated, but oil consumption via play in the valve guides is not a major concern. This would be a concern in a typical gasser car, which will have vacuum on the intake side, but not for a turbo-diesel. Vacuum on the intake side will try to pull oil down into the intake manifold. Simple physics, not really that hard to understand.