OK, didn't realize valves were in a cab, I thought they'd been outdoors since 1975. Just to be sure what you did to diagnose this, did you switch a different valve to this same cylinder, or did you just reverse the hoses? If you didn't do it, just as a double dog check I would connect this valve to a different cylinder and verify the cylinder has a problem. Also connect a different valve and make sure this cylinder works OK. If you already did that, then yes it probably needs some work internally, or at least I'm out of ideas. It's not hard to pull the spool out, just be gentle and make sure you keep everything really clean. Ask your wife for a clean sheet, they love it when you get hydraulic fluid on them. Once you pull the spool look for any burs or flat spots on the spool that might be causing it to not move all the way in one direction. You can clean the small passages in the valve body and the spool with solvent and compressed air. You can't hurt anything as long as you handle it carefully, it has very tight tolerances so you have to rotate and wiggle it around as you remove or insert it. The orings are probably hard, you can replace them but they only seal low pressure. Or you can just take it to a shop, they can test it on the bench and confirm there's a problem internally before they take it apart.
