W221 bork factor?

[Mogul]

Thinking about a W221S350 BlueTEC (2010-2013) and may look at cars from 40 to 100k+ miles.

Struggling to find much about the bork factor and/or real world maintenance costs - where should I be looking?

Are there any age/mileage related surprises out there? I've just replaced the belts on my 7yr old Discovery for example...

Hoping to find one with Distronic Plus but not that many about...