Right, I am looking to buy 330d I'd there any issues a should be looking out for? Dpf issues etc?

My own BMW is a petrol version so my diesel experience is limited to my family members 

My brother inlaw currently runs a 530d he commutes in to Europe for work and this car is approaching 300k his previous car a 525d went way beyond that, before the BMW's were a succession of Merc's. His service regime is meticulous with oil changes every 5k and the full BMW schedule followed as indicated plus gearbox services in line with ZF's recommendations.

Yes he has had niggles particularly things which BMW seem to ignore/deny/can't find or see mainly electrical, these we have fixed ourselves but mechanically the cars are mega. 

So History History history plus general condition always a goo indication that someone has cared. ZF recommend gearbox service every 60/80k BMW say sealed for life, for life read end of BMW warranty responsibility. Engine bay should be clean showing no signs of leaks. There was a problem with the tubular exhaust manifolds cracking (smell of exhaust fumes in the car) BMW solution was weld it up which proved temporary we found a cast manifold on the well known auction site which strangely was cheaper than the tubular manifold fitted, problem fixed for good. Both his cars have been remapped with no issues and the current one no DPF issues either. Suspension bushes last about 80k but are not difficult to change/up grade just make sure you have a full suspension alignment at each tyre change or suspension work to protect tyre life. Make sure all switches and gadgets work as they should.