At least once a year? Why so? My dealer said once every 5,000 miles or 12-14 months whichever comes first. For me, that is the 12-14 months as I don't rack up 5K in miles per year. Wish I could though...This is something you definitely want to do at least once a year. If you have never done it, just have a local mechanic do it for you, it shouldnt cost much. We do ours once a year on average, unless we pack up for a long journey, we may get it done before that too.