Have you dismounted it from the tractor yet? you won't know the problem until you start getting into it and You won't know if you can fix it until you get into it.I don’t know if it’s the lever or the valve but I’ve got to repair it somehow.
As was mentioned a few times, I would remove the cover over the joystick and move it in all directions checking for it to be hitting something instead of getting free and full travel. Also, try installing the loader with this cover off so you can see the joystick operation during the 'install' process. This is something you can do for free except for a little bit of your time. You may find a bent or 'out of adjustment' linkage that you can either bend back or readjust to get it working again. Something else to check, I know you said you have removed and installed the loader a great many times as have I with mine. I always remove mine for mowing with my finish mower so I can get closer to things and not take out fences when mowing alongside of them. I did this 2 weeks ago and left the mower in the shade all day under the carport. When finished and I went to reinstall the loader, I swore I had all the hoses fully seated by looking at them. But the same problem you are having happened with mine. I had the tractor off and relieved the pressure on the tractor side and was sure the hose pressure had not built up sitting in the shade. After a 1/2 hr of cussing, I removed the hoses and let out some pressure, then reinstalled. Sure enough one of the hoses seated further down than it was on the first attempt and everything went back to normal. Now when I 'know' I am absolutely doing it right, but it doesn't work, I just say to myself 'what simple basic thing am I doing wrong or missing?' Usually just going back through the process reveals the problem. Not saying you did something wrong, but it could be a couple of things to look at. Good luck with it and let us know what you find out.It appears from the picture that the handle is bent so far forward that it is hitting something (maybe the plastic cover) and not allowing it to move enough to allow the valve to pass oil.
I would try removing the cover and see if there may be an interference.