I wanted to check my trans fluid this evening and was very hesitant on taking off the fill cap. It felt like the rubber would tear if I tried to pry too much. Doesn't appear to be a screw on but more of a plug.
Crazy enough but I wanted to stick a meat thermometer into it to see how hot the fluid got. Appearantly when temps reach over 90 degrees, then that is when the oil breakdown begins. When I finished mowing, I touched the outside of the trans and it was HOT. If it was that hot on the outside, I can't imagine how hot the fluid must have been.
BTW, I have a x320 and cut a mostly flat acre with a slight slope (around 3/10 of the acre on a 10 degree pitch) in front yard. Can't imagine this overworking it.