Re: Hydro-Gear oil..which to use?
I have a DGT6000 with hydrostatic which I use for mowing and bulldozing in the summer and snow blowing in the winter. It worked great in the summer, but by the third winter the temperature went down into the teens and the tractor would move slowly going forward and just creep in reverse, both bad for snow blowing. It would get stuck on a wheel track in reverse and barely push into the snow going forward.
After much research, I went with Castrol Syntec 5W-50. It is the oil I already use in the engine and it works great in the transaxle, summer and winter. The transaxle had the same pep forward and reverse in the winter that it has in the summer and it runs cooler in the summer.
As far as the oil weights go, the second number in this application is the important one. It needs to be high, at least 40 but preferably 50. This is the viscosity of the oil when it's hot. The first number, the one followed by the W, is weight equivalent when the oil is cold. If you run it during the summer only, a 20W or 30W is fine. If you're looking to run it in the winter, too, you need to consider a 0W, 5W or 10W. Whatever you use, synthetic is better for the transaxle, and engine, than conventional oils.
As Alan Lloys said, the easiest/best way to drain the oil is to loosen the allen head screws and let the gerotor cover drop down, but be very careful to NOT let the cover come off. The oil will be draining very slowly so let it go overnight. You will get between two and four quarts of oil, depending on the capacily and how much oil is left.
You never mentioned why you're changing the oil. Normally, the oil is supposed to last for the lifetime of the transaxle, but that is not true, and it must be topped off on occasionally.