Remove the aluminum end cap from the valve. You will see a nut mounted on a threaded stud. There shouldn't be any fluid in this area, but there may be grease smeared on the spring.
Tighten down the nut until it is real snug. Don't tighten the hell out of it or you will shear off the pin at the end of the bolt that keeps it from turning. All you want to do is to bottom out the spring, so you will feel it get tight when this happens. Notice how much slop there is in the bolt and that it will turn with the nut back and forth about 1/4 turn without the nut even turning on the threads.
If you find that the nut was already tightened down and bottomed out, then that is probably the problem right there.
Using a marker (like a Sharpie), put a line or dot on the nut and the end of the bolt so you can reference them against each other. What you want to do is back the nut off 1/4 turn. Since there is a lot of slop in the bolt itself, observe the markings on the parts and back the nut off until all the slop is taken out, then make sure the nut backs off the bolt 1/4 turn.
Do not start the engine or turn the car while you have the cap off the valve.
In most cases, this will provide the correct amount of load that the spool valve inside the housing will center itself and both sides of the system will get equal pressure. Reinstall the aluminum cap and try the system out. If it still pulls one way, then the spool is not centering for some reason and you can try adjusting the setup again.
Try adjusting the nut only about 1/8 turn at a time and then test. I don't know which way you may have to adjust the nut, so you will have to experiment with your setup. If changing adjustments do not help, then there is something else wrong with the valve.
