Speedometer failure

[JGP]

I have an interesting situation with my '02 A6 quattro avant 2.7 Biturbo.

The speedo and odometer stop working and within about 5 mins the fuel gauge starts fluctuating.
If I disconnect the battery they will reset and then work normally for a period of time - not usually more than 10 minutes and then will just stop working again.

If I leave the battery connected and disconnect the instrument cluster power connection (Big blue one on the near side) they will reset and then work normally etc..

Ran a scan - no codes. All apparently fine.

The cruise control works (although I have no idea what speed I am setting it at.)
To my mind that rules out the VSS. So I assume that the cluster is at fault.
Does anyone has any tricks to rule out causes, Or alternately revive the cluster - Short of getting it overhauled.
Should mention that the vehicle was off the road for a couple of weeks and the battery ran down.
My feeling is that the cluster will behave "normally" if there is some way of hard resetting it after the battery failure.

Any ideas including witchcraft welcome.

[zollaf]

could be a cluster fault, maybe a scan would show something . you could always send it off to somewhere like bba reman to get it tested and fixed if it is found to be at fault.