A common issue we find with sprinkler systems is that Solenoids sieze up and allow the valve to leak by. This video is from Orbit and does a good job of explaining how to replace a solenoid. This installation can be applied to any brand of valve. We stock replacement solenoids of every major brand.
This shows how to adjust the Hunter PGP Rotor. Other brands are similar but my have a left fixed start vs a right fixed stop.