It's my understanding the exhaust is filtered through a particulate filter (that traps, then incinerates exhaust particles), THEN the urea is injected to the nearly clean exhaust to convert the nitrous oxide into water and nitrogen. After 1,600 miles, my exhaust pipes are as clean as a whistle.

If this is true, then the urea injection, and also the particulate filter, shouldn't decrease the longevity of the engine. I'm guessing these X5s will go 500,000 with proper belts, hoses, fluids, etc. changed before anything becomes a problem. I can't discern any 'cheap' or 'flimsy' short cuts in the design or materials that would hamper longevity (my opinion).

My VW's have been an '00, '03, and my current is an '05. They are phenomenal if maintained and a relatively cheap.

I've known folks with Mercedes diesels with 500k+ miles with only proper maintenance (no major parts replaced).