Hello and good morning Dave,
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I would start by removing the cable from the steering actuator and then turn the steering, it should turn easy side to side, if not then remove the cable from the helm unit and if still having a problem it is in the helm, if not then replace the cable (if binding) if neither are the problem then would need to check the belt tension not slipping on the pump and insure the pump is working also checking fluid is full and no trapped air as well as lines correct. It is true that it's not often an actuator goes bad, however it can happen and is usually in the tube, you can disconnect the actuator from the drive and (not in the water) turn the drive side to side to confirm it's pivot points are not the problem.
Turning hard lock to lock esp holding at a hard lock you should hear the power steering pump load up, if not there may be air or a bad pump or belt is too loose or not, however this can also happen due to the tube in the actuator and could also be a blockage/restriction in the power steering cooler.
It's pretty much a process of elimination and there are not many things to do just what there is to be done does require some hours of testing.
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