Hi Gary
If the fault is intermittant it looks like you have a problem with the shunt wires try taking them off and cleanining make sure you put them back on the same way as you took them off if problem still there you will have to go into the box and trace the shunt wires to the pins and clean and make sure they have a good contact the shunt wires will be on a copper strip and the colours are purple and grey fasten by two philip screws.
Hope this helps let me know how you get on