If that pump is one that is mounted just above the PTO shaft at the rear of the tractor, it is driven by a shaft with a rectangular tang, I think. That tang engages a slot in the end of the pump shaft. Your description of what happened with the pump and the QD's suggests to me that when the QD became disconnected, it deadheaded the pump and split the pump internally, causing it to leak oil from every orifice. The pump deadheading would put a heavy load on the engine and force the operator to run in a lower gear to keep the RPM up, which just makes the pump split sooner. This stall situation created by the back pressure of the deadheaded pump can also round off the drive tang.
The pump should remove easily with the four or six bolts that hold it to the tractor. Once those are removed the pump should just pull off and you can visually check the drive tang and slot.
One thing to note when/if you replace that pump - the rear pump rotates the opposite of the engine-mounted pump for the FEL and steering, from what I recall. You shoiuld verify this with the dealer you buy the new pump from so you set it up right. It isn't difficult to change the direction of rotation, you just sort of swap ends on the pump assembly.
