I would find the spec, and buy the EXACT lubricant they call for. A Hydro is the WRONG part to try and save a few bucks on. OEM filters and Fluid is all I will ever use in a Hydro.
IF yours calls for the newer Synthetic, stand by for sticker shock

If you are not 100% sure, contact a Cub dealer and have them look it up.
If you make a mistake there's no draining it and starting over with the right stuff. The damage will be done before you even know it.