Most only need cleanup and adjustment.
HERE is a rebuild kit. If it happens to have the original felt sector shaft seal that should be replaced by a newer style lip seal (SKF 11055) that was used on later trucks.
The engagement of the sector shaft with the ball nut is adjustable, and may actually be all that's needed. Check the service manual for the adjustment procedure. It can be done with the steering gear in the truck. It just takes removal of the pitman arm or disconnection from the drag link, and the use of a fish scale on the rim of the steering wheel as it's turning.
