Ben "Santorin LO"
Thanks Ian, Ric and Jacques, As recommended by Ian, the drive unit was inspected and one of the coils has lost its original form, was replaced and now working 100% (did 72hrs blue water sailing and another week coastal with around 100 hrs and not a single time lost course).
For the next ones: Problem symptoms were:
a. Auto pilot stopped working - with little push on the helm started again.
b. Auto pilot stopped working, no alarm sounded and no little push helped.
c. Under pressure (side wind 15 knots or waves on the side under engine) was relatively working ok - I believe this pressure replace the 'little push'.
Coil was relaxed on the drive and 100% performance now.