I have an original 1955 Eldorado engine. After having the carb rebuilt, i am told i should be using some type of Fuel Additive (original Valves) Do any of you have suggestions as to what type or brand might work best? any special suggestions? I am almost afraid to add something. The car has been working just fine for the last 15 years without any additive. You know..... if it ain't broke..... Thanks