Loose PS Box??

Good day guys. I'm on here asking a question for my son about his PS box. He bought a 71 Duster and has a bill that states the power steering box in it now was new or rebuilt in 2006. I tried to adjust the screw but it was already at it's limit. (well maybe only 1/4 turn until it bottomed out). The steering wheel has about 6 inches of play, 3 each side when car running. :wack:I noted that the pitman arm had no movement however the worm gear connecter coming out on topof the box was lifting about 1/4 inch when rotating the steering back and forth....We have no idea why a box would go bad in 6 years or so. However, My bet is it time for a new box.???

BTW We would rather go manual..new looking in Calgary Alberta area for a tight used one.