Often, the cable corrodes inside the tube from a lack of grease when put together,....
Look for a power steering unit just like a car. A reservoir and a pulley run by the engine belt.well its rack and pinion steering and not sure where about power steering fluid.
Well, with the cable disconnected just at the hookup at the transom, you turn the wheel, and see if it feels stiff. If not, its usually ok. Just checking the fluid, don't mean the pump is working properly either.