Just to be clear, are you referring to the gear box mounted to the frame, or the P/S fluid reservoir?

I assume the gear box, but just thought I'd ask the question...

I've never experienced any great leaks myself outside of a small amount of fluid I've seen around where the fittings for the lines are on the top.

I'd assume the seal on the bottom side where she connects to the pitman arm would be the most likely culprit. I've never seen on any of my vehicles, the input shaft leaking, but it's certainly not out of the question.

 

The P/S pump leaks. I had a bad one for a while. Replaced the pump, now the steering box leaks. Get ready for a PITA.

 

I've had good results using Lucas P/S stop leak.

 

Output shaft seal...easy to replace BUT to do it 'right" box should come off and clean/polish shaft.
Many I've seen the shaft is dirty/rusty and just slapping a new seal @ it w/o cleaning them up would almost guarantee a leak again.

Here is a before shot of what I'm talking about.

Mine leaked pretty good 7 months ago.
Removing the shaft, cleaning/polishing shaft, replacing the bearing and reinstall it is both leak free and way less shaft play.
Bearings are almost always worn as well.