There seems to be lots of "horror stories" about diesel beemers but the most are regarding the 320d, the 330d is much more reliable. I've had mine for a year and half and 30k miles with no major problems, there are a few "preventative" maintenance things to do though. I would do the swirl flaps for peace of mind, it costs £25 for the blanks and they're easy to change, you also want to change the oil separator for the newer "vortex" type as the old style gets blocked and kills the turbo, also a good idea is to bypass the egr valve instead of filling the inlet with exhaust crud, it will bring up a light on the dash but never bothers me, or you can get it mapped out whilst getting a remap. I would recommend a remap by the way! It makes them obviously more powerful, a lot torquier and smoother, makes them rev more like a petrol and improves the economy, for £250 it's a no brainer. The thermostat went on mine but was a £40 fix and I think I have a cracked exhaust manifold at the moment which is a problem with the 2004 models, the manifolds of that year appear to be made by toyosports! As with any car that age the bushes will also be getting past their best but the wishbone ones are the worst - which he has had done so bonus. The wheels are awful for corroding so check the insides of them, mine weren't holding air, also the front wings rust badly just above the wheels so check for bubbles, if they're not rusted and you buy the car whip them off and underseal them - they're a water trap so will rust otherwise. They're very good cars imo, comfortable cruisers, quick and good handling not the same excitement as a wee turbo hatch but mine would still keep up with a lot of them!