Manual steering gear- how long do they last?

[C10wip]

I have been working on tightening up the steering but there is still a little slop. Doing the steering wheel back and forth test, it seems that it's coming from the steering box. The first time I did that test I found a bad tie rod end, and replacing that which made a big difference, but you can still feel the slop when driving. I have also put in the XJ steering mod. So, my question is - how long does the steering gear box typically last? It's an '80, and I have no idea what the mileage is ( looks like a different inst. panel ) and the truck does not look particularly well cared for.
I have seen the warnings about doing the "bubba" adjustment on the screw so I'm not going to do that, and doing the proper adjustment means pulling it out and checking w/a dial or pointer torque wrench which I don't have; I don't want to do all that if it's likely that it is completely clapped out anyways. The rebuilt ones from RockAuto/Cardone are only $95 so it's tempting to just do that. Any advice?