Many Grasshopper owners have mentioned on various threads that they are aggrevated at paying high prices to get "Grasshopper" brand oil for their hydroststic systems and they can not get specs to find cheaper oil. Well, here is info you need so you can purchase replacement oil at more reasonable prices. My Grasshopper dealer, ( he is a former factory rep with GH), and his lead mechanic said the following oils can be used to replace the GH hydro oil: Mobil DTE 26 Quaker State AW ISO 68 My local oil distributer said all DTE 26 oils are the same and are identical to any of the oils that say AW 68; AW ISO 68; or just ISO68. MY oil dist. has been in the business for 45 years, so he ought to know. I bought a 5 gal. bucket of Duraguard ISO68 for 20.00. Thats a lot cheaper than the high dollar GH oil.