James Dean, Thanks for that David Petryk link. Excellent photos.
I agree w/ keeping the gearbox, since tight. Why trade for a worn rebuild? I have rebuilt several 1960's Mopar p.s. gearboxes, which look similar inside, so wouldn't scare me. They even show the same "adjust torque friction w/ weights" in Stretch's link, though I just used feel.
I would look for the source of the leak and try to fix w/ box installed. Often, they leak from the seal on the Pitman output shaft. Mopar guys replace that on the car. They remove the circlip, run the engine and lock the steering to build pressure and blow the seal out, which also helps purge junk. On these M-B boxes, even easier, since you unbolt that part for bench work as shown in Petryk's attached photo. In my experience, O-rings and shaft seals are generic, so perhaps not dependant on M-B supply chain.