Autohelm Raymarine - won't engage

[dfelsent]

I drained the hydraulic fluid by removing the spool valve and draining the fluid into a bucket.
I ran the pump in both directions and manually pulled and pushed the cylinder piston back and forth.
I ran the pump by telling the pilot to go on one course then another.
To my surprise there were black crunchy deposits in the reservoir. The fluid was quite yellowed.
I cleaned the reservoir and ran new fluid through the system. It came out clear from the valve opening.
I installed the new valve and topped up the reservoir. I exercised the system back and forth. I could hear the improvement as the air left.
With a bit of use the system finished bleeding.