My objection to ZDDP in a bottle is that it's typically $15/bottle and there's no indication of how much ZDDP is in a particular formula. It's also not widely sold at auto parts stores (at least O'Reilly, Autozone, Pep Boys). If you have found a good locally-sold ZDDP additive, please tell us where you got it.
Colo Springs, CO
'78 FJ40, '89 FJ62, '98 4Runner