How well does it work right now? Are the seals and bearings ok from what you see?
allow me to stick my nose in. Whatever the seals look like( and chances are they look fine ), they will be due for replacement and any decent parts store can match the numbers, they are standard seals and the set can be had for well under a hundred bucks ( I think I paid around $40 including a wear sleeve ) Open up the top cover and take a look , do not be frightened off by some chewed off teeth on the gears as long as it looks resonably balanced. REmember there are no synchros in these boxes and years of grinding has taken place ( and you will certainly add to that wear

Bearings rarely wear unless run low on oil.
There are no gaskets available except the pto covers, Spicer says to use Loctite 581 gasket eliminator , you'll need a caulking gun size tube to seal that box up
Whoever gets that thing, PM me for manuals, proper modern lube spec etc