Repair Hydraulic Leak (O-ring Replacement)

What happens here

The farmer removes the hydraulic fitting from the cylinder. Upon inspection, he discovers that the leak is caused by a broken rubber O-ring within the 'set nut' (which he clarifies is actually the part that tightens the fitting, not a set screw). He replaces the damaged O-ring with a new one. Then, he reassembles the fitting onto the hydraulic cylinder, ensuring it is snug but not overtightened.

Goal: Stop the hydraulic leak by replacing the faulty O-ring and reassembling the fitting.