Tractor Repair: Kubota mower deck, kubota gr2100, rear differential

Question
I have a Kubota GR2100. The mower deck will not stay up on its own. It is hydraulic, I can raise it but it slowly drops down by itself. I can see the rear differential slowly dropping. How can I fix this?

Answer
the hydraulic ram or ram seals are possibly worn remove disassemble inspect the seals and fit new seals it is possible that the spool is leaking back to the tank but i think this is less likely
so disassemble the rams and hopefully there will be an obviously bad seal