Well, there is a debate going on. I think Yamaha didn't use one for a reason. IMO, I wouldn't use one especially if you ride in hot weather. I had never used one in the 4 years I've had my Rhino. Of course, you get a little dirt in the CVT but it doesnt take very long to pull the cover and sheave to clean and re-grease. I do this about every 300 miles. Most of the time it doesnt even need to be cleaned.