[rodent]

I picked my scooter up from the dealers after having the "correct" nut fitted, the mechanic told me that the there is actually nothing wrong with "incorrect" nut and it is exactly the same as the "slotted or black" nut.

He went on to say that allegedly the problem was just that the nuts were not torqued into place properly at the factory.

Your mileage may vary.

PS: On my bike the nut cannot be seen through the oil level hole with oil in the bike.

Edit: I took my bike off the trailer leaned it over to the left to let any oil drain away, and yes you can see the nut through the oil level hole. It's toward the upper left.