Over the Counter Zinc Additive

You know all this hub bub about zinc, How many tens of thousands of flat tappet hydraulic engines are still running out there with nothing in the crankcase but whatever comes off the shelf nowdays. I don't remember hearing about a rash of flat cams since the early 80's when I worked at the GM store. Put a additive in just to be safe. I do but I don't measure it out down to the parts per million.