Synthetic oil does not cause leaks in older engines — this myth costs people money

The old claim that synthetic oil causes gasket leaks in high-mileage engines was based on early 1970s synthetic formulations. Modern Group III and IV synthetics are fully compatible with all OEM gasket materials. If an engine leaks after switching to synthetic, the gasket was already failing — the better cleaning properties of synthetic simply revealed it faster. Do not pay a premium for conventional oil out of fear.