when turned and held at one of the steering locks, does he pump whine and the hoses flex as if the internal pressure in the system is rising?
the only real way to tell would be to check the pressures. a gauge and some fittings is actually pretty cheap compared to changing a bunch of parts and not knowing for sure if those parts are actually faulty., a small piece of debris inside the valve in the box could be your culprit. a good reason to clean the area first before starting a job and also always flush the system with the return line dumping into separate container after a single part is replaced so that no contaminants have a chance to go downstream into the workings.
it is possible that the hydraulic valve inside the box is not working so the fluid is bypassing through the valve and out rather than through the valve and being directed to the appropriate side of the piston inside the box or rack.
https://www.freeasestudyguides.com/p...sure-test.html
https://www.hotrod.com/articles/ccrp...ering-secrets/