C'mon Rick....be a better adviser to us homeowners and stop posting only what you think is important. Look at the Index in the PDF then go to page 11 and read the instructions for changing the fluid. How many hours is he going to put on the ZTR per year....15? At least one can change the hydro oil every 3-4 years and keep it fresh. Without looking at the specs for the lawn tractors he's listed, I'd bet the only way you can change the hydro fluid is by physically removing the tranny and that is not something most folks want to do.
Hours have nothing to do with it, Hydro Gear themselves in there pdf Page 11 say:
The EZT Transaxle is a sealed unit and does not require oil maintenance. However, in the event of oil contamination or degradation, oil addition or change may alleviate certain performance problems.
1. Remove the transaxle from the vehicle.
noTe: if removing the wheel from the
transaxle, do so by removing the four (4)
lug nuts. do not remove the axle/hub nut.
2. Clean the oil fill port area of any debris.
3. Remove the oil fill port fitting.
4. Position the transaxle so the oil will drain
completely out of the housing.
5. Fill the transaxle at the oil fill port according
to Figure 4.
6. Install the oil fill port fitting.
7. Purging will be required. Refer to the purging
procedures on Page 12.
8. Recheck the fluid level once the unit has
been operated for approximately 1 minute.
As far as the 50" deck goes the op posted a link for the XT1 42" with the 18hp Kohler and that's what I commented on and it's probably enough for what he needs.