Re: JD175 Hydro (1988 model) Hydro transmission problems
there is a sticky about changing the oil in a K46 hydro at the top of this forum. though your hydro may be different a similar method would apply. remove it from teh tractor, flip it and drain it out. goto the manufacturer's site and get the specs, then refill it with teh proper amount of recommended oil. reinstall.
you say the oil looks thin, maybe it has a thinner weight oil or maybe it has had water in it. either way, teh best course of action for something so neglected would be to change ALL fluids, plugs, AND belts. even if they look ok, they are likely very degraded.