[tom406]

Everyone will be different on this one, but I don't use anything on my personal cars, even if I know there aren't hardened valve seats. If I was planning on hammering the throttle I might add a tankful of additive, just to be on the safe side, (its my understanding that aggressive driving causes more heat on the valve seat area, exacerbating the degradation.) But mostly I just figure I'll drive it until the seats give out, then do the proper new-valve-and-hardened-seats thing later, if necessary.