Is the ram (arm) unit inside or outside? If outside its possibly
water getting into the ram and damaging whatever senors/electronics are inside the ram to
monitor and control the ram position.
The other possibility is
corrosion in the
plug. Normally this results in the unit failing to move at all, but prehaps a bit of
corrosion and added
electrical resistance here is affecting the
rudder angle sensing system somehow. Easy fix is to bypass the
plug and hard wire it to the
autopilot control
head.
These tillerpilot type units are not particularly waterproof (having drowned two) They are more like splashproof so to protect the final unit a waterproof cover made from something might help, as well as limiting its use in severe conditions. Prehaps modifying the mount to get it inside, or up higher, or mounting it so the ram unit angles down and
water flows away from the vulnerable ram seal.
Matt (islandtime) on here knows a lot about autopilots. prehaps worth a PM.
I dont know how you dissasemble them, but this might be an option on a dead unit to at least determine if its water ingress. Sometimes you get lucky and can dry out and clean up wet and corroded
electronics and get a bit of extra life from them.
Have a look through Webb Chiles blog. He has had multiple failures on his
small boat round the world. Probably up to number ten unit by now..
Sounds like a hard trip. I can't begin to imagine how hard rowing across an ocean would be.