Stopping a hydraulic oil leak in a Massey Ferguson tractor can be a tricky business. The process depends on the source of the leak. If the leak is coming from a loose or damaged fitting, the first step is to tighten or replace the fitting as appropriate. If the leak is caused by a tear in a hydraulic hose, the hose may need to be repaired or replaced. If the leak is caused by a broken O-ring, the O-ring will need to be replaced. Lastly, if the leak is caused by an insufficiently sealed surface, the surface may need to be cleaned and correctly sealed with liquid gasket to stop the leak. In any case, it is important to ensure that all parts of the hydraulic system are properly cleaned and maintained to ensure the system runs smoothly and safely.