1975 cj5 steering box leak

Hi guy's i got a leak on my steering box (saginaw) on the end cap. I've seen on the web we can remove the cap and change the seal on it. But i would like to replace cap and seal but i can't find any replacement part. A friend a mine gave me a steering box from a jeepster commando and i wonder if i can use the whole steering box (when he took it away from the commando he weren't have any leak) or can i just use the cap on this one and use it on my existing steering box?

ThanK's for help guy, i really appreciate it!