John Deere Z Trak z820a Hydro question

I'm trying to change the hydro fluid in my z820a. I've never done it before and can't seem to find any info online for this type of mower. Does anyone know how to do it and what needs to be done? I'm about to go look at my mower again, but looking at the pictorial parts catalog on John Deere's site, I'm not seeing a hydro filter. Is there not one on this mower?

Next question is about the caps on the top of the hydros. The parts catalog doesn't have a part number beside the caps. Does...

John Deere Z Trak z820a Hydro question