I like to drain the old junk out, put in a couple or 3 quarts of kerosene, jack one side of the tractor up so 1 rear wheel is off the ground. Spin the wheel by hand for a minute or 2, let the jack down and do it all over again with the other rear wheel off the ground. Drain it all out, let it drip for as long as necessary, re-fill with your choice of gear oil. I like Mobil 1.