yeah be very wary of injectors not sure how you can detect it tbh. Mine had the ecu light come on a week after I got it and the car went into limp mode. What year is it? the 03 plates had bosch injectors(very poor fail all the time) the 04 and onwards have delphi injectors which are a big improvement. When they go they just go tbh the only real way to check that I know of is to get it plugged in on diagnostics and get a injector check done. These are great cars when there running but cost an arm and a leg when there not(im sure all new diesels are the same though). my advice is take it for a decent test drive make sure it doesnt smoke at all. make sure the engine is dead cold when you start it up and that it starts up first time without any smoking. Mine used to start badly on a morning then once started would start up with no smoke at all. kev if you need any advice on these if you do get it, give me a shout as Ive done a lot of research on these while I had mine.

Edit: also EGR valves tend to go at some stage and can be quite expensive. When I bought mine I took the inlet off and cleaned out all the crap inside just incase so it didnt knacker the valve.