[CA] [CA11] ST5000+ Control Head malfunction verification

[avalonS211]

I have a ST5000+ auto pilot with Mechanical Type 1 Drive on a 36ft sailboat.

the boat is new to me, I believe the autopilot was fitted at some point in the late 90's maybe? (Not sure the release date of the ST5000+)

Anyway....It is not functioning properly. I have spent quite a bit of time reading here and going through the troubleshooting steps listed in other posts, FAQs and documents.

Here is what I have found:

1. The FluxGate compass is okay. The testing with multimeter showed the proper readings.
2. The FLuxGate compass does need to be relocated as a AC unit was installed recently and is under the sink where the compass is.
3. The failure modes on the autopilot are: the dockside rudder calibration fails. The procedure starts with short stuttering moves to starboard then it goes to lock and reverses, once on port lock it just keeps trying, it does not return to center, and I hit STANDBY and cancel the calibration.
4. Sea Trial compass calibration works and finds 33 degrees deviation. which is high and expected due to the AC unit too close.
5. Hitting AUTO underway the autopilot goes full when it makes the first course adjustment.
6. Rudder sensor functions.

Questions:

1. Is the control head at fault?
2. Is it worth it to relocate the compass and try again or is the failure mode more and indication of a failed control head?
3. Is there anything else I can look for? Drive connectors?
4. How does the unit know when rudder has reached full lock? Is it in the control head or is there a sensor in the drive unit?
5. How do I verify the drive unit is sound for continued use?

I am resided to the fact I will be replacing all of the system or parts.
Option 1 is to replace with the EV-100 Sail wheel pilot. More affordable.
Option 2 is to verify Type 1 drive is good for more years of use and go to the EV200 system pack (more expensive but retains the Type 1 drive, rudder sensor)

Help much appreciated...