I looked that up on the internet and there was an exploded diagram on a 'Motoruf' website: that looks like a mechanical unit (as opposed to hydraulic), and that suggests a mechanical clutch rather than a hydraulic one. That's good news as the hydraulic units are generally harder to repair from what I've heard (lots ov very small bits that are easy to lose on disassembly).
But i couldn't really see a clutch in the diagram (nor engine for that matter) so probably can't help you.
I assume the clutch is a hand lever that you squeeze to engage drive and let go to stop? If so I can only suggest the obvious then, that the clutch has been stood for a while in the disengaged position and it is just sticking:- can you follow the control cable to the clutch and observe any of the mechanism? Does it feel normal when you operate it?