350SDL (gulp) question

[DslBnz]

Yes, the 350SDL.
What a wonderful car.
It purrs at idle, almost inaudibly with zero sound insulation.
It achieves fuel economy equivalent to the 3.0 liter.
It is very quiet and refined at speeds of over 100 miles per hour.

It also loves to bend rods 50% of the time on original motors. Ooops!

This particular one's different. FAR different from mine and its obnoxious nature! Remember that black 350SDL I was driving for a stint? Well, it's developed the classic insatiable thirst for synthetic blend diesel oil.

There is almost no blowby.
The intake manifold, and crossover sections are clean as new.

She starts up instantly. No skipping, but a constant cloud of blue at idle when warm or cold.

Consumption? Average city 50/50 highway mix = 220 miles per qt. My father and I (he's driving it now) took it down on a business trip to Connecticut at about an average speed of 75 mph. IOW, 100% highway.

Consumption? Highway 100% = 130 miles to the qt.

You'd never know it. What could it be given the available data? Could it be the headgasket oil passage being blocked? There is NO BLOWBY in this sucker. None!

The engine is pretty smooth at idle. Almost inaudible. But when it is revved, I swear I hear something that resembles a heavy metallic lifter-like clank at the front of the engine. But it could be me and my paranoia getting the better hold of my conscience.