When I talked to the great guys at Teleflex across the "pond" they told me to remove the hydraulic lines on the sides, then remove the fitting the lines attach to(in my case the 90 degree ones). Once the fittings are removed you will see a light spring that has a steel ball behind with a case and o-ring it on each side. Clean the ball, spring and the seat the ball sits in. On our boat the autopilot cause the upper helm to turn as it pump fluid.
They sell new springs, balls and cases but he said it is rarely needed unless the parts are damaged.
See the attached PDF they sent me. Worked like a charm with no parts....