You do not need to add anything to modern oils for flat tappet motors. Its a myth that you need it, and even back in the day ZDDP was added to prevent oil oxidation, not to reduce wear. Initially it was, but the uber high levels (1000ppm+) were not for wear or tappets, but for controlling oil oxidation. This is straight from GM engineers and the report is readily available online.
Modern oils have taken out ZDDP and replaced it with other additives. Modern overhead cam engines still use flat tappets... and millions of flat tappet motors are being made today.... from I-4s to V-8s.
Nothing you add to your oil will stop wear. If you want to do something to slow down wear, get a pre-oiler. Its a documented fact that 90% of wear occurs at start up. Pre-oilers get the initial oil film created much sooner than the oil pump.
Please do go to Bob is the oil guy.. they will back up what I have said.
