question Zetor Proxima Hour Meter Fault

I own a 2008 Proxima 8441
Have the tractor about 6 years now.
When I bought the tractor the hour meter did not record hours.
The Rev clock is working fine.
I think but cant be sure that the previous owner was told by his dealer that he needed to replace the whole dash clock unit.
This was fairly expensive.
I belive the dealer tried to repair it or something before I got my hands on the tractor but it was unsuccessful.

Does anybody know is there a common fault with these clocks?
Could it be the sensor. If so where is the sensor.

I wouldn't be familiar with a Proxima, but the Forterra range from them years the clock would be all the of the dash and couldn't be separated. The some of the models then had digital hour clock and now they all have them, so the roller numbers are gone, but of those type that did have roller numbers they did get stuck and it wasn't uncommon to see a tractor not move past 2500 hours.