I managed to find a working odometer for my 260E....but the speedo is reading 10-12mph faster than I am driving when comparing to my GPS.

Is this something that I can fiddle with to calibrate or will it require professional calibration?
I am okay with it being <= 5mph, but 10 is quite a lot more than I would like.

Any info would be much appreciated.

Thanks,

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k