AC 6040 lift going up on it's own

I just got this tractor on a trade, the Piston that raises the lift arms was in a box and came with the tractor. The tractor ran fine everything works good except for the lift. He told me that he tried to fix it but after he put new seals on the piston when he started the tractor, the arms went all the way up and crack the top of the Piston housing so he took the Piston out and it's been in a box ever since. I thought I would see if I could get it back to working cleaned everything as best I could put new seals on the piston new o rings where I found them and just as he said arms went up on their own to the point of the Piston being in a bind against the housing both levers were in the down position. Also after shutting the tractor off the lift will not lower. Any ideas?

Never worked on a 6040 in that area. Generally speaking, the lifting system has feed-back linkage to see to it that cannot happen. I'm sure it worked fine until it was taken apart, the linkage didn't get assembled correctly and now we have a broken housing. When you pull up on the 3-point lever the hitch only goes up in relation to where the lever is. Half-way up on the lever and the hitch goes half-way up and stops, etc, etc.