Oil comes out of the plate when the tractor is running. The cotter pin was sitting on the plate when I found it. The hole does not appear to be threaded so I don’t think I am missing some kind of plug. Maybe this is where a medium PTO would connect?
I have checked the fluid levels and nothing is out of place. The oil was maybe 3/8 “below its level. I am pretty sure it is engine oil as it is much darker than my hydraulic fluid.
At the same time that I became aware of the oil leak, I realized that the tractor was overheating (I let the radiator screen drown a lot).
That is a “drip” hole to indicate gasket leakage. The cotter pin is intended to move and prevent mud or other debris from clogging the hole. If it is under the clutch housing, it would indicate a leak in the rear engine main seal or transmission input shaft seal.
With the engine running, if the oil comes out, # 1 checks if the engine crankcase ventilation system is blocked. If the ventilation system is OK, you have a leak in the motor seal. If only a small amount drips; a 1/4 teaspoon or less in an hour, idling, oh well, oil is cheap.