“The manufacturer has to prove the additive caused the damage.”
No they don’t. They can deny your warranty on a whim, and then YOU have to take them to court. Then, MAYBE they’ll have to prove their position.
You're going to have even less time if your oil pressure is actually low and you spin a rod bearing.
https://www.harborfreight.com/engine-oil-pressure-test-kit-62621.html