Purchase and locate all necessary replacement parts. Put on protective eye goggles and gloves. Set up a box or protected surface big enough for all parts, those for replacement and those removed from the tractor. Turn off the tractor and disconnect battery cables.
Use appropriate wrenches to remove the PTO cover. Place bolts and cover on a surface as the first parts are removed. Note the location and placement of the gasket on the cover. Remove the shaft from the bearings and gear box noting the condition of the key in the shaft. (Some do not have a key depending on the model. Those need to be oriented exactly the same in relation to the gear box.) Take out the O-ring, washer, parts and bearing. Inspect all for wear and note worn spots.
Replace the O-ring, washer, parts and bearing. When installing the new parts or re-installing the old parts, be sure to clean surfaces and free up movement when necessary. Take the new shaft into the gear box and confirm proper fit and movement. Coat the cover gasket with proper gasket cement and lay it on the cover. Bolt cover into place and torque to 80 pounds.
Confirm that all bolts are tightened down. Ensure all shields, covers and safety devices are in place. Reconnect battery cables. Turn on the tractor and then confirm the PTO is working properly and there are no leaks. Attach a small device to the PTO and confirm proper operation with no leaks.