Simplicity ZT Mower - Change Hydraulic Fluid?

[Elklake]

I just purchased a used Simplicity Model ZT - #1693475 zero turn mower. It has the fixed steering column with two paddle handle type controls, with a Kohler CV16s motor and a 44" deck. I am doing all of the routine maintenance items and I need to know whether or not I should change the hydraulic fluid. No reference in the owners manual other than to top off the fluid if it is low. I could not find a drain plug on the hydraulic drives.

Should this be changed? I do not know how old the mower is but I am guessing around 6 - 10 years old. If I should change the oil, how do you do it?

Thanks for any info you can provide!