Over the Counter Zinc Additive

It's the old Kendall Oil refinery.... IIRC, it had a mediocre reputation back 40 years ago.... I can't say these days. We use the Brad Penn break-in oil, but for regular running, I'd prefer a different brand.... just my personal opinion. The right levels of ZDDP for flat tappet lifters/cams is a key to have, regardless.

If the Brad Penn that you have has the right levels of ZDDP (1100-1500 ppm), then that has one advantage in that you are not putting in another additive that could possibly work against the additive package already in the oil from the refinery.