My Lt 1000 craftsman would barley move auto transmission. Fluid check looked like milk. Everything I read said no oil change possible. Oil should last a lifetime of transmission. Hydro Trans get very hot causing condensation. Was told must pull out Trans to change fluid. Right under the hydraulic release lever there is a flat spot on the case you can drill and tap a 1/2 inch hole for a drain plug. Then remove the fill plug on top of unit toward back of ring gear area . Remove battery box to locate refill with 20/50 oil 87 2.7 qts. I recommend synthetic. Jack up rear of tractor to fill . Purging air out is the hardest part with the right wheel off the ground you can start mower and purge air by putting weight on the seat put in gear and let run until the wheel start to turn when the whining noise stops air should be out of system. Drive it forward and backwords a few times and it should work better than ever before.