I think it was more that they didn't want customers to have to fill it, as it's just one more annoying maintenance item to take care of it. I've never seen any

I think it was more that they didn't want customers to have to fill it, as it's just one more annoying maintenance item to take care of it. I've never seen any warning or notice stating that it should not be filled by owners. I have a diesel VW and refilling the tank is pretty easy. The dealer didn't have any qualms selling it to me.