59th AE has started being hard to steer, fluid is at half full mark, no sign of leaking.
Inspect all power steering hoses. Replace as necessary.
If the steering fluid has never been changed, first thing I'd do is flush the system and refill to the full mark with fresh fluid. Bleed the system according to the Service Manual. Then road test. Drive the car a while to warm the fluid then compare the current steering feel with what it was before.
If, after flushing and refilling, if steering effort is still high, you may need to replace the pump and or the rack.