The decision to do this hinges on how long each of us decides to keep the X5. If you're in for the long haul, this might be worth the extra upfront cost to avoid the replacement costs of future air spring leaks. I like the idea that it can be done to keep stock ride height or if you want it for performance and aesthetic reasons, lowering it.

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2000 Z3 2.3 Steel Gray
2004 X5 4.4i Jet Black