I just have the dealer do it once a year when I get the oil change. Its pretty cheap. I think the best substitute for gear oil however is to simply get rid of the oil,chain,and gears and have a belt drive. I know there are a few drawbacks, but for trail sleds, I bet it can be done. Just get rid of the whole, potential leaky cover, bad gears,weak chain,adjuster,weight,,etc. I work with BIG machines with a lots of installed horsepower and many are driven by toothed, herringbone style belts and some of them last YEARS,running 24/7. Just a wish. :snack: