More gearbox woes

Once again more gearbox problems from my friend Tony, out of a different bike - affectionately referred to as *hitbox. He'd been aware of something untoward for a while and after some minor investigation found that the output shaft nut was loose causing a noise/sound something akin to a slide hammer in action. He tightened this up to discover that the box was even less happy and so the bike was stripped apart. Pricing up used parts and a gasket kit those alone were going to be approx £200 so he's put the rebuild on hold and is going to use a spare gearbox