The mobil oils I've purchased by the gallon from Enco with discount and free shipping are about the same price of mineral based motor oil locally. Most I've bought on sale and they were considerably less than local oil. No need to mention the high price of synthetics. You don't have to use what's recommended, and there is likely a better oil than what's recommended, but you should use an oil designed to work with the application. I'm still looking for a good open gear grease available in less than 5 gallon pails. Prefer a cartridge or a small tub.