Over the years I've used Miller's Diesel Plus in our diesel cars, mainly to lubricate the injector pump rather than seeking extra performance. We have just bought a Kia Cee'd 1.6 CRDi, and the handbook warns of invalidating the warranty if additives are added to the fuel. Also, I was spotted at our local Shell filling station using the Miller's additive, and was told that V-Power already had the same ingredients. Is putting in the Miller's a waste of time? I still worry about lubrication of the pump and its longevity.