Take the clutch cover off and check the belt and the clutch faces. If the look ok, you might need to replace the wet clutch or a least give it a look. Have you used syn oil in there. If it is not wet clutch approved, it will slip too. I don't think the parts are going to be expensive, but I don't live in AU. Look over the manual and you should get idea of what it will take to get it fixed. I don't think it will be anything major, just time.