They should be the standard saganaw 76 box seals. Same as the ones found on, say, a 1978 cj5. Check at your local auto parts store and compare the shaft size. You may want to pull the box and determine where you have a leak. If the box still operates well then fix the seals. Could simply be the o-rings on the hoses. Might just be the output seal........ Both are the easy to replace. Give it a good visual once-over before you tear it apart.
The two best off-road vehicles in the world -- the Jeep CJ and rental cars.