Since people go around telling the world about buying avgas and race gas for their street car, nobody wants to risk the high probability of then trying to explain it to the revenuers...
Beside your wasting your money anyway. Fuel has been reformulated several times since the 60s. If/when the rubber parts deteriorate, replace them with new. Sometimes its a pain but its still cheaper and more convenient for a street car to be able to buy at the pump.
