Are you discussing the front end loader or the 3ph?
If the 3ph, kebo might well have the answer although the rockshaft valve knob should cut off all movement if it's closed (so the lower links (arms) shouldn't drop even when you do move the rockshaft lever). Can't hurt to open and close that knob a few times.
If the loader, it's probably the hydraulic valve.
However, always do the least intrusive work first. That means to check the hydraulic fluid level first. If the level is correct, change the hydraulic oil and filter (clean any screens in the system too). If that fixes the problem, great. If it doesn't fix the problem, then you'll need to decide if it's a problem you can troubleshoot or if you need to take it to a dealer.
tdquarterranch, you will need the tractor maintenance manual if you want to tackle the job. And I suggest you do not start tearing anything down until you confirm parts are available.