It's not going to be easy to put a value on it since market on these is all over the place. From my own experience I missed out 2005 4.8is with new transmission and all service records from new 89k miles that seller was selling for $10k just 8 months ago. So I ended up getting 2002 4.6is with 75k miles and two owners with extensive dealer service records for $7500 this past July. You best bet is putting it up on eBay and let market decide. Or list it here where people know what it takes to keep these on the road and can appreciate a taken care of example.

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2002 BMW X5 4.6is