I do not think you have hydrostatic steering but instead a regular steering box with the power steering build into it...
From the WSM:
This integral power steering mechanism consists of the following two major components as shown above: hydraulic control valve and steering force assist hydraulic cylinder. The control valve is housed in the casing and composed of sleeve (3), input shaft (1) and other parts. The hydraulic cylinder, on the other hand, is composed of gear box (7) (cylinder tube), ball nut (4) (piston) and other parts. When the steering wheel is turned, the reaction force from the tires is exerted through the sector shaft (6) onto the main shaft (5). The torsion bar (2) is then twisted to make a gap between the input shaft (1) and sleeve (3). Such gap activates the valve to switch the oil flow direction. The sector shaft's pinion, which comes in mesh with the ball nut's rack, is tapered along the teeth. In this way, the sector shaft (6) that turns by the adjust screw (8) changes the clearance between the rack and pinion, adjusting the play of the steering wheel. (Tighten the adjust screw and the play becomes smaller, and vice versa.).
Dave