Not knowing the state of my valve seats, I was using a lead substitute with every fill up, now I use some Lucas injector cleaner. It is professed to work the same way and it worked wonders on my Ford pick Up to clean the calves and injectors, a night and day difference. So I figure it can't hurt. I also use 93 octane gas. The literature that came with these cars called for 100. I don't drive them enough for it to matter much. But if the gas is going to sit for a long while, I do add Stabill-the new blue stuff-for ethanol gasoline.