I have one.
Bought it in 2013 from our local MB dealer with about 70k miles, so too many to be CPO.
This model does not have the DEF system. It does have the DPF. Dealer replaced the dpf as part of the pre-sale fix n flip.
I have done the following:
Oil Cooler seals (I contributed to this thread, my posts starting about page 4 or 5).
A journey into the the infamous Om642 oil cooler leak!
Had to replace the steering rack
Normal maintenance (brake pads, it takes 19" tires so they are on the expensive side)
Glow plugs
Not too much else
My son has about 160k on it now, still doing well.
The only thing about these is the interior trim is not as high quality as found in the W166 (the successor model that went from 2011 to 2018). Lots more cheap plastic.
Also be sure to look in the arm rest and make sure there is a device about the size of a small candy bar that is sitting horizontally on the shelf. This is your Bluetooth adapter for your phone. This car was designed back in the day when there was a bespoke Motorola flip phone designed for this car (that does not meet modern carrier standards for E911, plus it's a flip phone). So they brought out this module to plug in to the dock for the flip phone that allows Bluetooth connectivity with any phone. This only allows Handsfree profile, it does not support A2DP.
They did produce a dealer installed accessory box that allowed you to play your 30 pin iPod through the sound system. It will be in the glove box if the car has it. Hint, the cord for this is long enough to be rerouted up into the center console compartment where it is much more convenient. And you can attach a 30 pin to Lightning connector adapter and a short Lightning extension cable to this and it will allow you to use a modern iPhone.