While under warranty ALWAYS use the manufacturers recommended oils. There is not that significant savings to use a cheaper oil and if you do have to go in to a service center for warranty work they will have (1) less out for helping you with getting a repair covered under that warranty. After warranty, use the same oil. It's still cheap compared to a new Hydro or a Hydro repair. Most ZT's are above $3,500........isn't it worth $35.00 for oil for maintenance? Your peace of mind is not a bad thing either.