Well, I got the stuff to do the Hydro Fluid and Filter change and what a pain in the behind!! I ended up jacking up the front end and setting the wheels on cinder blocks and then jacking up the back and resting the frame on jack stands with further support via ratchet straps connected to a header in my garage ceiling. The left rear tire had to come off in addition to the seat and rear fender assembly. The gas tank gets moved out of the way as well. Per a recommendation that I found online I blew the whole area out with a blow gun really good before I started.
A couple of lessons learned: filling from the fill line only really works IF the check port is open at the same time. Also, the schematics from the Hydro Gear manual are a bit confusing as they do not appropriately illustrate where the fill and check ports are on my machine, or at least in the configuration/orientation of my transmission. Lastly, if you have fluid to spare, flushing the drive is highly recommended!
I am going to guess that the service on this transmission either had never been done before, or if done it had been a really long time. The fluid that came out was thick and black. Since I purchased 5 quarts of oil I ended up flushing the transmission twice with warmups in-between before finally changing the filter and filling it for the last time. The first flush came out nearly as black as the initial drain, then the second flush more of a dark brown. Once I finally changed the filter and topped off the oil after a few bleeds/purges, the oil in the transmission was golden yellow.
Following that, I adjusted the drive mechanism as the machine would creep in neutral. There is not a lot of adjustment so I ended up having to back the linkage all the way down to stop the creep. Before I put it all back together I will be replacing the fuel line from the tank to the fuel pump and replacing the transmission cooling fan which of course has no fins on it!!
I am hoping that after doing all of this I have a much smoother, quieter, and more reliable hydrostatic!