These are throw-away pumps and not worth rebuilding because the cost is too high.
Click on the link below.
Click on hydraulics on the right side of your screen
Click on pumps on the left side of your screen
Click on gear pumps --same side
Scroll down to the D Series pumps and you will see the D27AA2A pump.
You can buy that pump for less than $250.00. It is the same pump as in your tractor now except that you need them to supply inlet fittings for it because this pump has threaded holes on both sides. Your pump was special ordered with an inlet fitting but you can"t buy that pump from anywhere but the dealer and it will cost you twice as much there.
When you change out the pump, make sure you empty the oil out of the system and then refill it with 20W50 or 15W40 motor oil. Do not use hydraulic fluid.