Hi Dermot,

There are known issues with these engines, but mostly if they're not serviced regularly or driven at higher speeds often. So for example, the EGR valve and DPF can clog up, as is common in many modern diesels.

BMW has had issues in the past with timing chains stretching as well, plus the turbocharger itself can have problems, leading to excess oil consumption and even loss of power in the extreme. 

These problems don't affect all examples of the engine, but fussy about service history and condition if you are considering one, and give it a thorough once over before buying as well.