That's called a "manipulation dot" and is to be steered clear of at all costs (if you ever want to resell). It occurs when a used odometer with lower mileage than the engine (ECU/BCM) is installed. If you use an odometer with a higher mileage, no dot appears.

The "right" way to do this repair is to buy a new cluster and have it coded. This particular truck could have 200,000 miles on it... who knows. I thought it was illegal for a dealer to sell a vehicle like this without stating the mileage is unknown or something.

Edit: Still looks like a nice truck... if he would sell for $4000-5000 I'd still go take a look. But I doubt that's the case.

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2005 X5 4.4i Build 04/05 Maintenance/Build Log
Nav, Pano, Sport (Purchased 06/14 w/ 109,000 miles) (Sold 8/15 w/121,000 miles)

2006 X5 4.8is Build 11/05 Maintenance/Build Log
Nav, DSP, Pano, Running Boards, OEM Tow Hitch, Cold Weather Pckg (Purchased 08/15 w/ 90,500 miles)

2010 X5 35d Build 02/10
Nav, HiFi, 6 DVD, Sports Pckg, Cold Weather Pckg, HUD, CAS, Running Boards, Leather Dash, PDC, Pano (Purchased 03/17 w/ 136,120 miles)