Carbon deposits, especially on the EGR (exhaust gas recirculation) valve
If driven for a lot of short journeys, the engine’s internals will get very dirty from soot, and the diesel particulate filter (DPF) may get clogged
If the engine is not allowed to cool down after long/hard drives, the turbo will get burned out
Timing chain issues, which seem to occur more on the N47 than N57:
Worn tensioners (recall issued in 2015)
The timing chain itself often has incorrectly machined teeth and often is overstretched, which causes premature wear. Replacing the chains (there are two) is a huge job because they are located on the back of the engine, and the sprocket is machined directly onto the crank…which means you will need a new crankshaft.