The reliability (or otherwise) of the car will depend on the engine type. In my opinion, the M52TU was bulletproof, mine has over 170,000 miles on it and still runs like a watch. The M54 seems to be similar, but the N52, which used Valvetronic variable valve lift did not enjoy such good reports. The M52TU ceased in 2000/2001, and the M54 was discontinued in 2006. The N52 was used from around 2004 onwards. All these engines have chain-driven camshafts. There is a school of thought which recommends chain replacement at 60,000 miles, and (certainly on the smaller N42B20 4-cyliner engine) there have been modifications to the tensioner over the years. A new tensioner is a few tens of pounds, so whenever the camshaft covers are removed, it is worth inspecting and replacing, especially if it is still the unmodified version in place.