You have the Hydro-Gear EZT ZT2200 transmission. It is called non-serviceable by Hustler and other. B.S. It was designed to use 20w50 Castrol motor oil. Any 20w50 can be used. You can easly remove, drain, and refill in about 4 hours. Most of the time is waiting for oil to drain. When I change the oil in mine (I got water in it) I removed both units as an assembly. Left the tires on and rolled it out and over two containers to catch the oil. Removed the plugs and rolled it up side down. Waited 2 hours for drain then refilled with an old gear oil bottle with bottom cut off for easy filling. The spout is the most important part. It fits the hole and allowes air to escape at the same time.
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Forgot to say I got some paint filters from auto parts store to filter oil because it needs to be clean.
I also wet the garage floor so it would be less dusty.