I have my doubts about the newer engines lastly and having a good reputation. The V6 is not a smooth motor and has post injection cycles that wash down cylinder walls, dilute oil, lots of blowby even with new engines. All for emissions...the particulate filters need raw fuel to heat up and burn off the accumulated soot, and Mercedes does it with the main fuel injectors not something downstream of the engine. Of course fleet vehicles will be okay for alittle while as the rack up the miles fast, but personal ones will likely die young from uniformed ownership and poor maintenace.
It is reported the newer MB specs 229.51 are NOT great oil for long intervals, it is missing most of the additives that other diesel oils have in the name of the particulate filter lasting. Yet somehow Mercedes allows 10k mile oil change intervals (even longer on some). Forget about fixing one the current V6 diesels, no factory supported parts for engine internals! Some valve train, some other things but no big rebuilds. Maybe aftermarket will kick in, but then there is always a quality issue. Price a turbo also, it will get your heart rate going!
Getting rid of the DPF and the post injection cycle seem to be the keys to long engine life, then oil choices are wide open also.
I think in 20 years these will be long forgotten engines, killed away by emission regulations and high maintenace costs. I own one too, but am taking steps to ensure it will remain a good engine for some time which few will bother with.