If my memory is still sound, on the x250 the speed signal is derived from the ABS wheel sensors, so no discrete sensor, unlike the earlier x244 which has a discrete road speed sensor.
Whatever the source of the signal, the analogue presentation depends on a small electric motor (stepping motor) which is electronically controlled and is what moves the pointer.
On motorhomes which typically spend long periods laid up the pointer / motor spindle tends to stick, If this is the case then it is possible to remove the instrument binnacle and either make a DIY repair, or send it to a company called "Cartronix" for repair.
For the brave, the DIY route involves removing the transparent cover and gently nudging the pointer to free it.
If removing the instrument panel, I advise disconnecting the starter battery first, by following the procedure in the handbook, which allows the vehicle computer network time to shut down.