No, the GPS is going to be accurate to several feet. The odometer has additional gears that aren't involved in the speedometer indicator, even though they are driven by the same cable. Do a search in the forums for odometer problems, I know there have been some. In my '87 190D, the odometer drive gear moved on its shaft and became disengaged from the driven gear. The odometer stopped working entirely. I was able to push it back in position and it's been OK, but I imagine the gear can simply slip a little on the shaft but stay engaged.

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1987 W201 190D