Better living through chemistry. If you buy a higher end name brand
oil, you do not need any additional
oil additives. Lubricants and the additives have improved tremendously over the years. Why do you suppose OEMs recommend you change
oil every 7,500 miles in a new car today, much different than 30 years ago? They have found additives perform better in your engine. They did the research, advertise and charge extra for the oil.
Gasoline is so much cleaner burning today than it was 15 years ago and the EPA required Deposit Control Additives (DCA) in gasoline. The EPA requires the gasoline DCA to be certified by actual engine testing to prove it will keep your engine clean.
FunFer2's comment => "When I broke a rocker shaft with my 428 FE after only 2,000 miles and removed the heads, the amount of carbon build up was shocking ! "
What brand of gasoline were you running? I wouldn't use it anymore. I've heard ethanol can cause more valve deposits in an engine than regular gasoline. I don't know about methanol.