if it's like most it has a one-way clutch, this can slip either because of the oil (probalby not) or because of wear or becuse the clutch cracks like this:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=15570&p=576368&hilit=fusin+hose+clamp#p550415
someitmes you can fix them like this
https://endless-sphere.com/forums/viewtopic.php?f=2&t=86124&p=1260122&hilit=fusin+clutch#p1260122
https://endless-sphere.com/forums/viewtopic.php?f=2&t=15570&p=576368&hilit=fusin+hose+clamp#p550415
someitmes you can fix them like this
https://endless-sphere.com/forums/viewtopic.php?f=2&t=86124&p=1260122&hilit=fusin+clutch#p1260122