Maybe i should add. neither of those mowers were new. Both very used when I got them. 1st one, had no hood, but decent function till hydrostat went out. 2nd one, needed a starter, and something else? and I got it for free, in return for trailering their new Craftsman riding mower for them.
There is no way to change hydralic fluid, and I think that's a built in limitation. The engine, components are readily available. Decks, you can replace bearings, belts, even electric clutches, but once the deck is too far gone, a replacement deck costs 75% of what a new mower does.