Dealer should be able to sort you one for about £3, failing that get one from Wemoto for about £8 inc Del.
Whatever you get make sure that it's not the original 9mm one but the 12mm nut with part number 90891-10124, like the one you get from Wemoto. Not a big job but you'll need a 32mm socket, and a torque wrench setting of 90 Nm, check the manual for the exact setting (I think the original spec was 70 Nm for the 9mm nut but I think it was upgraded to 90 Nm for the 12mm nut)
Whatever you get make sure that it's not the original 9mm one but the 12mm nut with part number 90891-10124, like the one you get from Wemoto. Not a big job but you'll need a 32mm socket, and a torque wrench setting of 90 Nm, check the manual for the exact setting (I think the original spec was 70 Nm for the 9mm nut but I think it was upgraded to 90 Nm for the 12mm nut)
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