More fuel for the zinc - zddp war

[austinsailor]

https://www.hemmings.com/blog/2012/10/18/tech-101-zinc-in-oil-and-its-effects-on-older-engines/?fbclid=IwAR32gY2KcZHQ7CTFvSrbzv72Nq-UA0-rB2pKYh8KYEH9mz0dS6lethJFoEs

[greg g]

Half can of STP with oil change will address any concerns.  But with the light spring pressure typical in flathead engines of our era, it is not likely a critical concern especially in occasional use vehicles.  Most of this concern was coming from folks modifying engines with flat lifters, higher than stock valve spring pressures.  The issue was wearing high lift camshaft lobes prematurely, usually in aftermarket owner installed "high performance" pieces by manufacturers using who knows what for metallurgical specifications.  Several sources say that zinc and phosphorus were introduced into motor oils in the late 40's early 50's but I have never seen a difinitive date of introduction to the general public..