I've had many of the pre 80 series boxes open for seal replacement... not terribly difficult. It would be best to pull it out of the truck.
I recently obtained an FZJ box and Toyota has changed the upper bearing/seal area. If the seal is simply worn and bad, it should be an easy R&R. If you have play in the upper shaft, a seal alone may not do it, for long. Not sure how the adjustment for the shaft takes place on the box... maybe shims? The early box has and easy adjustment.... Sorry, it's early, and I'm still sleepy.
Yeah the shaft has no play so I think it is just the seal. Is that hard to replace? And can I get the seal by it's self? I was told not to mess with the steering box. That it is a pain in the butt to work on.
Well, just for you, I ran out to the garage and popped (partially) the section off the 80's box that contains the input shaft and seal. Look like you'll have to do a basic break down of the box, R&R most of the guts, then press the input shaft and bearing out of the housing to get to that seal. If anyone knows different, please chime in! The 62 and earlier box is much easier, just spin the large bearing preload cup off the top, R&R the seal, and back on.
You should be able to get just that seal. If you go for the break down, make sure you keep things extra clean.