Althugh they can be rebuilt if you only need bushes, bearings and seals, if the worm and sector are worn or their surfaces are breaking up, you will have to find another to refurb as these parts are NLA. The sign of a worn box from the outside is less than a couple of visible threads above the lock nut. They can still be smooth with only one thread showing but usable adjustment is finished after that. If it's leaking, replace the lower seal at least. A box with no oil will wear very quickly.
Anyone scrapping an Amazon or 1800 should always save the steering box for future use or parts recycling.