53+ don't use gear oil in their hyds. UTF fluid is better bet. no wonder you can't get em bled!
.. bleeder id a plug, likely inverted head , on top of the back area of the pump.. at least if it is a piston type.
loosen plug to help bleed.
if it was my tractor i'd drain that oil and put in utf. OR.. cut it with a couple qts atf-f or other 10w oil.. or a quart of kerosene... sump can hold 12qts easilly... 8 is normal fill.