Back in the day, the "common wisdom" held that switching to synthetic from dino would cause leaking because synthetic did not condition seals as well a Brontosaurus Squeezings. Then, high-milage oils ( eg. Valvoline MaxLife) touted their seal conditioner additives as the secret to Eternal Engine Life. However, if I am using an API approved national brand Group-IV oil, should I be concerned about the heartbreak of dry, flaky, cracking seals flooding my engine with unwanted ooze? Can I supplement them with "over the counter" seal conditioners?