I have the same problem with my wifes 98 ML320 with 85000 miles.

The oil consumption is increasing a lot when driving long downhill roads and using the engine/gear as brake. This could normally indicate worn valve guides. However, I read somewhere that there have been issues with the inlet manifold gasket on the 320 that fail and suck oil into the inlet ports during these driving conditions.

Anybody with more info on this?

Per.