I add a bottle of ZDDPlus at every
oil change for all my flat-tappet engines. Avoid engine oils that have the "energy conserving" API donut on the back label, as these oils typically have reduced levels of
zinc. Oils that are approved for diesels (API CG4 thru CK4) have higher levels of
zinc and anti-wear additives, so I look for oils that are approved for both diesel and gasoline service - API CK4/SN. (API-SN rated oils are approved for gasoline service). If you want to learn more, check out the Petroleum Quality Institute of America at pqiamerica.com They have a lot of info on the subject. Regards, Scott