Small Engines (Lawn Mowers, etc.): Toro Wheelhorse 1638 Hydrostatic Transmission, mobile 1 synthetic oil, gear box assembly

Question
My Toro makes a roaring noise when the transmission is placed in reverse or if I'm going downhill at less than full speed. Could the transmission be low of fluid? How do I check/fill the fluid?

Answer
 Hello Joe:

 You can View this Mower at this Addy https://lookup2.toro.com/partdex/index.cfm?xCaller=Toro and Enter the Model Numbers 16380. Then Select your Model. Then Select Gear Box Assembly. The Cause of the Noise is the Worm Shaft and Gar has Excessive Wear. It May Also be Low on Fluid. Diagream #36, the Plastic Screw should be the Fill Plug. Fill with 10W30 Synthetic Motor Oil. I use Mobile 1 Synthetic Oil. Fill to the Bottom of the Threaded hole. If the Noise Persists, then the Worm Shaft and Gear will need to be Replaced. Hope this Helps. I am here if you Require more Assistance. Let me know wat Happens, Please. Thanks.

 Good Luck

 Respectfully

 John