The loader valve is just a dual remote valve with a mechanism for allowing the joystick to rotate in any direction. The internal valve and return spring are very similar to the single remote valves at the rear of the tractor. There could be some internal binding in the valve, but my guess is that it's the linkage as PineRidge stated. If you remove the rubber boot and look at the mechanism while moving the joystick, you should be able to see what is causing the joystick to bind. Some spray lube might help also.
I could post the exploded view, but it's not as clear as just removing the boot and looking directly at the dual valve.
Does the joystick not return to center/neutral when released? I had to disassemble one of my rear remote valve return springs and lubricate it. Since the joystick valve has the same mechanism, it could be related to water getting into the valve and causing it to stick. /forums/images/graemlins/confused.gif