Antony, you're a star! 2 x M8 rivnuts[1], and it's all tickety-boo. Very simple. Clutch plates are soaking in fresh oil. Old clutch plates looked a little dry, if anything. Clutch centre has slightly polished sections, rather like "stepping" or "notching" but only visible, rather than tangible, iyswim. [1] which is what were used by the manufacturers, it would appear.