Ryan - I have used both Shell Donax TD and Mobilfluid 424 for my 129's with no problems.
But, Hytran at $9 a gallon isnt a bad price. If the cheaper hydro fluid is not from one of the major oil companies, its best to stay away from it. The fluid may work, but have reliability problems down the road. The better fluids have a naturally higher viscosity index, additives that allow entrained air to disapate faster,better seal compatability, flow thru the filter better and handle water vapor better.
But, Hytran at $9 a gallon isnt a bad price. If the cheaper hydro fluid is not from one of the major oil companies, its best to stay away from it. The fluid may work, but have reliability problems down the road. The better fluids have a naturally higher viscosity index, additives that allow entrained air to disapate faster,better seal compatability, flow thru the filter better and handle water vapor better.