The chain has to be lubricated every 200 operating hours with any special chain spray lubricant resistant to high temperature as the grease can come into the friction linings of the clutch.
Firstly, remove the PTO protection (make sure to place it back again when you finish lubricating the chain). Clean the chain before lubricating it. Avoid applying lubricant to the places where it could spill to the clutch from.
If the lubricant gets spilled into the friction linings of the clutch, the pulling force is reduced and the clutch plates have to be replaced.