The ZDDP carrying product like Rotella 15-40 was requires by the manufacture of the cam and lifter kit for My 460 ford Motorhome . I needed to supply receipts for two fill and change quantities or they would not honor any warranty. The reasoning was the ZDDP protected the lobes and lifter faces long enough for them to work harden I stayed with the rotella for 70,000 more miles and never had an issue. Stayed with what worked. Fortunately the motorhome did not have catalytic converter so the ZDDP was a non issue.