First of all, that swivel fitting has been seeping for a long time. There is so much dirt covering the nut up you can barely see it. You will need a new fitting and o-ring. Now, why did it fail? Harmonic vibration of hydraulic oil causes that every time. Does this tractor have the correct steel tube between the junction block and swivel, or a shade tree hydraulic hose ? Is the junction block bolted solid to the clutch housing or bolt broken or missing ? Early tractors had a 90 degree elbow at that location which required beating the lift arm off the shaft to service the pressure control valve. The swivel feature cured that problem but requires other parts to be correct. Hope this helps.