That's a lot of years. I think mine is slowing down going up hills, that scares me because I don't know how to service the non-serviceable transmission. I think some guys actually tap fittings into them to drain/change the fluid. It's only 5 years old but I do pull a big cart behind it sometimes and mow up some fairly steep hills, will have to figure it out.
I just changed the hydro fluid on my JD. It was the non-filter/non serviceable unit but online shows 2 bolts to take out of the housing that go into the sump to drain the fluid. It was pretty easy.