Not unusual for this to happen.
Kubota's spec is a little more liberal than I'd like to see and I understand why.
I'd like to see zero drop in 3 hours but that's not gonna happen
cylinders and valves have tolerances. There is a such thing as tolerance stackup. So what the dealer would do if it were out of spec is to remove the cylinder and inspect the bore, the piston, seals, hoses, valve(s), everything. Almost always it's a cylinder bore, piston, or seal issue that causes excessive leakage. You would have to isolate which cylinder is the leaker and that's not exactly easy to do unless you have some JIC fittings.. What I always did was to remove the two hoses from one cylinder on one side, plug the hoses and cap the cylinder fittings (remember they have to be metal/high pressure plugs and caps--plastic ain't gonna cut it here). Then lift the loader, shut the engine off and let it sit. If it leaks down quickly, the cylinder that is still functional is the problem. After, I'd usually do the same process with the other cylinder and see if one is the leaker and one was good, or if both were leakers. At that point you know which cylinder is the issue and you know which one to deal with.
Always a good habit to put your implement on the ground when you ain't using it! The manual tells us that. Did you read it?