So I ride woods on my 2009 rmz 450. While out riding the other day I stopped to take a break. Just a couple minutes. When I started back up I had zero back brake. As I headed back to the house it started working agin. When I got back I Checked to see if I was low and topped it off . Had it happen agin today. I assume the fluid has broke down and I just need to flush it out and replace with new . Just curious if it could be anything else?