I just replaced my steering box with a reman from my local parts store and started having the same issue last weekend. I never had this occur before and figured a reman was a factory box that had been rebuilt. I only had a 17mm wrench on the trail when it happened to me so couldn't get the angle to tighten it correctly and was hoping it was just loose. The jam nut works fine driving around normally but as soon as I try an obstacle the nut backs out and fluid drains. If I figure it out I'll let you know, please do the same
I guess I should follow-up on this thread I abandoned a while ago
On mine, the nut backed out so far I was worried about getting it adjusted properly again. It was also under warranty so I just took the box in and had them swap it. I never had this problem with the stock box either, but mine was a factory solid axle so I had to swap the box when I went over to crossover steering.
After going through 3 steering boxes and having the same issue I added ram assist and haven't had any issues since.
It would be great if you could figure out the cause in case others have a similar issue - I know I'd love to understand the root cause.