Been driving the 49 for about 15 years on unleaded with a 1956 235". Have not touched the valves or seats yet. Only do about 3000 miles a year however.
At one time I was concerned about this and met ths old gentleman who seemed quite knowledgable on the topic and he told me that he put in a cup of ATF in the tank each time he filled it up. I tried it but thinking a cup would be good, a quart would be better. Not! The truck shook, smoked, popped and ran terribly until I ran the gas thru. So I don't know if the ATF would help or not but I have not done that trick for a long time. And as was written above, if you are not driving at sustained high speeds I would not worry about it.
Bill
