You have found the right forum. Peruse it, grasshopper, and you will learn what you seek. Yes, E53 X5s suffer from the same auto tranny issues as other bimmers of their era using the same trannies; leaky power steering/rack issues occur; they suffer the same electronic glitches and have door carrier/window regulator issues; and the awd system [transfer case and cv boots/joints] can develop problems over time. Some of the V8s are more problematic than the tried and true 3.0L six. If religiously serviced and maintained throughout its life, can you get 200-250k miles out of it? Sure - but at this point, 7+ years after the last E53 rolled off the assembly line, you will roll the dice to find one fitting that description. I bought mine with 81k miles on it, and expect to drive it till 200k+.

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2006 X5 3.0 6-spd w/Evo UUC ssk
sport/premium pkgs
born Valentine's Day, 2006.