My feeling is that as steel valve seats are already fitted, although how hard they are I am unsure, fuel additives should not be necessary for the low mileage that I do in the car, especially at the steady speed I drive it at, however I still use an additive to be certain. Another reason I use an additive is that I believe, rightly or wrongly, that the additive will alleviate the problems of the hygroscopic nature of modern petrol causing corrosion in the petrol tank. Any thoughts on this?