I don't know anything about your specific Robertson drive, but in general, these hydraulic drives have a reversible electric motor
driving a hydraulic pump that is engaged by an electric
solenoid controlled valve.
If you are hearing noises from the motor
, most likely it needs servicing. Sixteen years of moderate to heavy usage is about the expected time for them. Like any electric motor
of this type, it has brushes
and bearings with defined lifetimes. These motors are very easily serviced and brushes
and bearings are relatively inexpensive. Depending on your skills, this may be something you can do. If not, any good electric motor
shop or, probably, autoelectric shop can service
Brushes at end of life could explain your loss of power and wandering. Grinding noises could be bearings or a brush end bottoming on the commutator. Clicking noises could be the solenoid engaging as normal, then disengaging because the motor is drawing too many amps or not responding at all due to needing service
(that would be expected behavior for it).
It is unlikely the actual hydraulics are the problem.