e28 econometer question

Lately I've noticed that the econometer appears to be sticking, and sometimes it does not move at all when the engine has been turned on. Usually it moves about a fair bit reflecting the load conditions - throttle
position, whether accelerating, going uphill, etc - at the time. I've had the car for nearly even years and this is a new (to me) occurrence.
Anyone else had the same, and how expensive is it to fix?
TIA
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Could be the first sign of failing service indicator board batteries.
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