The reason behind some people not having locking caps from what ive heard is that Fiat decided there were going to use a neck with a one way valve in it which obviously means it is very near impossible to steal fuel. Although, as many people have quite rightly said it doesnt stop people putting something in, and this is why now all new grandes come with a locking cap. I dont even no why they bothered with the valve in the first place.
Rich
Rich