I have the same issue on my '76. Need to fix soon. Here is what the esteemed Pin-Head posted on this topic recently (note you can find this and more info by doing a search here on 'steering box".
Welcome to the board. You'll be amazed how much info is here and how helpful people are.
Pin-Head Said: "They normally leak from the sector shaft seal. The sector shaft is where the pitman arm attaches with the large nut. Often the seal leaks because the sector shaft bushings are worn out. Have someone rock the wteering wheel back and forth while you watch the end of the sector shaft. If it wobbles back and forth as opposed to rotating, then the bushings are bad and will need to be replaced and honed to size by a machine shop first, or the new seal will likely leak.
Changing the seal is a job because you need to remove the pitman arm. Buy or rent the beefiest puller you can find. Tighten the puller than whack the side of the pitman arm with a hammer and repeat until the arm pops off. "
Oh - you can buy these parts and also view good parts diagrams on SOR.com - that is also a very helpful resource when you need to see how things go together in schematic form. Note you can buy many of these parts new via CruiserDan on this board or also used via SOR and several other vendors (cruiserparts.net, CCOT, RockyMountainCruisers, JTOutfitters, CruiserSolutions, and more).