B&G autopilot fault

Since I had my 411 I have had a intermittent fault on the autohelm I just put it down to life! But slowly it's got worse, so time to investigate.
Checked the motor with a 12 volt supply, worked fine then the solonoid on the ram [BE CAREFULL AS THIS OPPERATES PAST THE ENDSTOPS IF YOU RUN TO THE END OF THE STEERING RACK WITH SEPERATE POWER ] Mine checked out ok, so I remember washing and greasing the steering mec last year and the fault went away for a few weeks so found the rudder drive sender unit and checked it sprayed it with WD40 presto! woked fine and no rudder error sign, removed said naughty sender unit and put a metre over it as per the manual and bad segments so no signal to the autohelm. Rang B&G and £200 sender unit to fix problem, ho hum !