Hi, Timbersavage. The whole Galion grader line were not bad machines. They just don"t exist any more because they were not up to the same standard as Caterpillar"s machines. I found the ones I operated to be fairly robust and basically better machines than quite a few others on the market at the time, just not in the same class as their Cat competition for handling, reliability (Although still way ahead of some of the others.), vision from the seat and the general "feel" of the machine.
I would just about bet that the auto transmission on your T500 is supposed to run with auto transmission fluid, just like Gatractorman said he took out of the one he serviced. A LOT of the early machinery auto transmissions used auto trans fluid.
Hope this helps. Happy grading.
You have a wonderful day.
Best wishes. Deas Plant.