I think to make it easy, you should sell the optiMax and get a yamaha. Just kidding. I have found (around here at least)it is much cheaper to get your oil from a dealer or service center too. They get it in Bulk. I get mine from a service/dealer and save quite a bit from buying it a store - they get it by the barrel and will fill up a milk type jug for you. This way you know you are getting the right stuff and saving a little too.