So it seems to be a thing! After hearing a noise, I removed the front sprocket cover to find the nut just sitting loose on the end of the shaft, not a hint of thread left in it. I bought a new nut from the dealers and came on here looking for a torque figure for it, turns out its a common fault and that most people, including Yamaha, know about an upgrade to a wider nut.
So how come my dealer in Carshalton sold me a 9mm nut and claim no knowledge of any other part, the dealer in Twickenham also claims ignorance, and even Yamaha UK say there is only one part number suitable for a my bike and that's for the 9mm nut I've been given?
Despite all the related threads on here I couldn't find a part number mentioned for the 12mm nut, is it a genuine Yamaha part?