If your dad chooses the Lucas additive, it looks like 1/4 of a bottle (4 oz) is quite adequate to raise the ZDDP levels to the 1200-1400 ppm range or thereabouts, which is the ZDDP concentration range where most motor oils used be. Too much ZDDP has been documented to cause its own set of issues; the whole Lucas bottle will raise it to around 5000 ppm per the Lucas documents, and that is way too high.