I had a look on Raymarines FAQ re Wheel pilots and here's their answer
"If your 4000/ST4000 wheeldrive continually disengages on it's own, it is most likely due to improper belt tension" They also go on to say that it needs to be serviced by one of their agents.
However I have also heard that its caused by wear in a cam, Raymarine have brought out an improved drive unit that can be retrofitted, my guess is that its improved to cure this problem.
I've just let my ST4000 steer the boat from Tampa, Florida to St Tropez, France (5500 miles) through some good and not so good weather without jumping out of gear once though it did shred a couple of drive belts and a drive cog.
Have you tried replacing these to see if you can get a little more belt tension to hold the clutch lever over.
There is a new conversion kit but its not cheap!
on a slightly different tack...have any of you tried both wind and electic self-steering and if so which do you prefare and for what reasons/conditions.....????
thanks