I would make sure that all the hydrulic pressure is off by cracking the hose to coupler , 2 tap it back in and disconnect, then I would go and buy a new coupler for the machine as the little balls have possibly damaged the coupler creating a bur internally, that way I could return the unit in the same condition as I received it.
I have seen this happen where I worked also skid steers that had hydrualic hammers would wear out the quick connect couplers, they would also break internally and act as a check valve when you would go to operater the auxiliary function, and the littler balls that would retract to make the connection woud hammer in to the collar and bur up to where it would interfer with coupling and uncoupling and I have seen couplings damaged the same way by hoses getting snagged and had to replace couplers.