Rebuild the auxiliary control valve on the side of the touch control. All fluid has to go through there to or from the reservoir.
There"s a block that both hydraulic lines go through. Located between the seat and shifter. It designed to slow down lowering the fast hitch so you don"t drop a heavy implement and damage it. Bypass that. I bypassed mine years ago thinking I"d fix it. Still on my to do list. As the fast hitch works so well I may never get it done.
In my limited experience with 3 super C"s and a 200 that will solve your problem.
So far any cylinder I"ve had leak down has leaked externally and was obvious that was the problem.