My 69 302 has 178K on the motor..heads have never been off. I have changed cams a coupla times and internals are super clean and still strong. Uses absolutely no oil. My question is what motor oil to use considering the hi mileage and original valves/seats. Oil was changed every 300 miles since new...I am second owner since 1994 and change it every 2000 miles. Any additives?