As dkrajcovic said... Just replace if you can find one reasonable. I have overhauled many a Saginaw box, and it is tedious at best. And the kits alone are near the cost of a good junkyard box!
Saginaw boxes generally aren't troublesome, so having one that leaks and has problems is not common.
clay there is a seal on the sector shaft you can change out pretty easily without completely tearing the box down but i'd go with an upgrade or a replacement box because there's a reason its leaking like a worn bearing or shaft and you'll come out ahead to do an upgrade.. plus you'll have the leaky box to try and fix for a spare...