Now that most of the oil makers are being forced to take out zinc compounds (ZDDP), we have aftermarket ZDDP additives available. For old engines with flat tappet cam design, ZDDP is important to prevent cam scoring. Anybody know what the best level for ZDDP is? I recall about 1500 to 2000 ppm was the right ballpark. Is there a downside to adding to much? I seem to recall it caused some kind of problem. maybe you oil experts could clue us in as to the specifics of the ZDDP thing.