ZL-20 FEL lost Hydraulic Pressure

I assume that the loader has quick connects, I would check those first. but the problem as you describe makes me think pump, unless there is air trapped in the system that it has not purged. if you can plumb in a pressure gauge somewhere that should be under pressure on start up should be helpful. does the three point lift work ,I think everything runs off one pump ,power steering does too.

which jinma model is it ?

the problem with the quick connects was not that they leak , the problem is that they fall apart internally in some cases , others have stated that the chinese rubber hoses break down internally and pieces collect at the quick connect and plug the flow of the fluid. I believe that your tractor has a screen hydro filter ,I think under the floor boards? if you have not looked at it in a while it might not hurt as then you will know if there is stuff in the oil floating around. good time to check the condition of the oil too, moreso if it is stored in the weather and not under cover. but you never know it might have been air that has worked its way out since it has restored function. when it was rebuilt the oil should have been drained and changed so it really should be ok one would think.