Look on and around the motor and pump that sends pressure to the jacks. There should be a tag or sticker that specifies what type of fluid that should be used. Otherwise, call or e-mail the manufacturer of the jacking system to get recommendations. The fluid itself will be available at just about any auto or truck parts dealer, Walmart or Target store. Use caution, as the wrong type fluid cam permantly damage your system, and void any warranties. If you are unable to location this information, your best option is to seek a qualified repair person or shop.