DT466E with disappearing oil

There are three places where the high pressure oil can mix with the fuel.
Leaking injector O-rings the high pressure oil manifold and the injectors them selves.
If an injector O-ring is leaking it will erode the O-ring away fairly quickly and result in
a hard start then no start condition. The gasket under the high pressure manifold
could be leaking even though it was recently replaced. Although unlikely the high
pressure manifold could have cracked and is letting oil into the fuel. Since this
happened all of a sudden I can't see it being worn out injectors.
If it was a single internal injector failure I would expect you would have a weak
injector resulting in a rough running engine.

I would start by replacing the injector O-rings and replace the high pressure manifold gasket and see if that fixes the problem. Have a really good look at the machined surface
of the high pressure manifold to see if there is a crack in it. The torque on the bolts
and the torque sequence on the high pressure manifold bolts is very important!
There is upwards of 4000 PSI pressure in the manifold.

Cleanliness is extremely important when working on fuel systems.

 

Yes, like mentioned, high pressure oil is leaking past a failed injector oring back to the fuel tanks.