Hydroboost Steering Box Help

[48cj2a]

Having an issue with my 85 CUCV M-1009 (Blazer)

There is a 1/4 play either direction with the wheel before the steering actually moves. Driving you must constantly steer left to right to stay going straight as it is wondering.

Today I swapped steering boxes with another hydroboost truck but his one was a gas 1 ton vs my military rated 3/4 diesel. At first start it would not pwr steer at all so I checked the p/s fluid and it was nearly empty so I filled it and although I did not actually drive it it feels no different. backing up and pulling forward. When I shut it off it started overflowing foamy p.s fluid.

Is there a difference between gas/diesel steering boxes? the casting numbers on the boxes were identical. Looking down the hole of the non pressure side looked like a check valve might have been in it. Is this correct?