I found the tag on the transaxle and it confirms it is a Hydro Gear 314-0510 166768 as expected. I looked it over and there is some leakage from the brakes. I don't know how much is coming out but it doesn't have a bunch of debris embedded in it, so I'm wondering if that happened when they grenaded the spindle. I don't see anything on quick inspection that looks problematic other than the evidence of a leak.
As for topping it off, it appears the filler is on the forward side of the fan blade and with no way to remove the fuel tank, I guess I'd have to access from underneath somehow. It looks like access to the rear would be by removing the back plate on the frame, but that doesn't appear to get me anything useful. I just pulled the wheels off my other tractor for the first time in probably 20 years. It obviously required a puller tool so since I already have it, I'll go ahead and pull these wheels too which will give a little clearance hopefully.