Please tell me straight up why steering box leaks?

[Razorhunter]

So I've researched this previously on other forums and still not sure what is causing my 3rd Gen steering box to seep atf4 out the top of the box. Thought it was running down from up top at reservoir but I'm 99% sure its just slightly seeping fluid from the top of the steering box.
I see only that threaded "adjustment? stud protruding so assume this is the culprit.
Noticed reservoir was pressurized after each drive/trip I took, so I did the reservoir cap mod to allow more clearance/venting of the little rubber vent inside. This seemed to help but steering box still seeps a bit out the top somewhere. Is there a way to easily go into this box via the top cap screws and replace a seal etc?
Or is this a complete removal/teardown of the box procedure?
Finally, what does that stud actually adjust and how is this setting calculated/determined?

 

[seafish]

There is an o-ring that seals between the Rez and the box...it eventually tends to leak but can be replaced if the box is not showing other signs of wear.

 

[Razorhunter]

What is the REZ? Never once seen or heard that term mentioned in all my research.

 

[seafish]

What is the REZ? Never once seen or heard that term mentioned in all my research.

rez = a misspelled shortening of "reservoir"