Are you adding zinc additive to your motor oil to keep the push-rod engine happy? As overhead cam and roller lifters have become more prominent, the anti-wear high pressure additives have diminished in current oil formulations.
No, but I read about it and know I should. Thanks for the reminder!
Additives are basically a snake oil. They might have a placebo effect on you, but most likely to ruin mechanism in a long run. At best there would be none long term effect at all.
There is no need to degrade modern oils, they are way ahead than even a decade ago on all terms. If you got a proper engine oil you can be sure you can run your engine safely even in Antarctic. Transmission is a different case, you still need to be careful with it, but quality synthetic fluid is more so a must if you are in a cold winter.