What is the recommended type of oil and grade to be used in the 20 HP Kohler engine in my Model 13076 GTX 20 Troy Bilt Garden tractor. The tractor is used in North Dakota. What is the oil capacity of the engine with filter change? What is the oil capacity of the transmission on this tractor? Does the hydraulic system and the hydrostatic transmission share the same oil? This type of information is missing in my Owner/Operator Manual.