Bottom of lifter worn thru

Zinc and other break-in additives aren't just for break-in. They also help protect the parts throughout their life. The main thing is the cam and flat tappet lifters. While it's most important to get those components to "break-in", "wear-in", etc., during the initial start up, the high pressures causing metal-to-metal contact between the cam & flat tappet lifters remain and needs to be addressed. So High zinc oils are recommended to protect those parts at the contact area. No other areas in an engine are subject to such high and concentrated loads. Newer engines aren't as critical because they often have roller lifters.

More info from Amsoil:

[ame]http://www.amsoil.com/techservicesbulletin/MotorOil/TSB%20MO-2007-08-08%20Flat%20Tappet.pdf[/ame]