Oh man, Steering problem

Sounds like that valve is sticking in the housing. The "pin" that comes up and engages the valve is moved by a thrust bearing trapped between two reaction springs. When you turn the wheel, the worm shaft (input shaft) develops end thrust against the ball-nut (think of holding a nut with a bolt threaded into it). this moves the thrust bearing (and the pin or lever) in the direction of the thrust. There is not a lot of force delivered by the lever, so the valve must be very free to move.

The valve is simple spool valve. In its centred position, it connects the right and left turn chambers to inlet and exhaust oil - keeping equal pressure on both chambers. As soon as you move it the slightest bit (a few thousandths of an inch) it partially blocks the return oil from one chamber and opens it to the supply from the pump. At the same time, it opens the other chamber more to exhaust (return oil), and cuts that chamber off from pump supply. Pressure builds on one side, the ball nut moves and removes the thrust from the pin, allowing it to re-centre. Valve goes back to idle (straight ahead)

If you take the plug off the end of the valve housing and carefully slide the valve out, you can clean it and check it for burrs or nicks. Some crocus cloth is good to polish it, like you would a valve in a transmission valve body. Check the housing for burrs too - cleanliness is critcal here - the clearances are 0.001" or less in some cases. No lint from cloths, steel-wool or any else that can jam the valve. Make sure the valve moves very freely before you put the housing back on.

sorry if the explanation is long... I believe the more you know about what is happening inside, the better you are able to figure out how to fix things.
Also - this is all from memory - I haven't been inside one of these in 25 years or more. If someone else is more up-to-date, please pitch in!