st5000 plus

[pirahna3]

Hi,
First time posting. I have a ST5000 plus autopilot. worked well up until putting the boat in the water 6 weeks ago. Had a pretty bad leaking steering cylinder so changed it as it had to be done and i thought air might be the problem.
The issue- when operating the auto pilot on standby or auto, it will only steer to starboard.
I have switched the drive polarity and it will then send it to port but not starboard. The - (minus) inputs are not responding.
-The rudder indicator is working and showing correctly
-Allthough I'm along side while doing these tests, i have set it to auto, and while inputting the minus in increments of 10, the compass reading on screen reflects the inputs. Then if i manualu steer to the port and go past the compass reading the auto will then energies the auto helm to correct back to starboard. but never to port
Any ideas???