As far as oil additives go I have only used one on the 440 in my 67 - that being some stuff called Avblend which is made for aircraft engines. I read the independent lab tests which validate the claims made by the manufacturer. I used it because I had a lifter that was sticking after a cold start - poured the stuff in and in about a week no more noise and the engine ran more smoothly overall. This is not a cheap additive and apparently has been around since before WW2, it costs $ 20.00 for a 12 oz. can unless you buy a case then it's $14.95. I have another mystery which seems to defy solution- I just had the chunk and the axle bearings replaced on the 67 the pinion bearing went out on the old one. However, now I have a new noise - when I make a right turn at high speed or slow down to come to a stop I hear a rubbing or grinding noise from what seems to be the drivers side rear a sort of wump wump sound. Has anyone had this experience? If so please enlighten me. Thanks in advance for any help. Marc 67 Crown Coupe