I typically add some castor to my fuel if it doesn't contain it already mainly because of reading on here how harmful fuel containing no castor can be. I can honestly say that I ran many, many, many gallons of Cool Power through a number of engines including my OS Hyper 50 in my Raptor Heli WITHOUT a SINGLE problem of ANY kind bearing or otherwise. I genuinely feel the castor is a good thing and will continue to add it if not already there but I will also feel quite safe if I have to fly a gallon or two without it because of an availability issue. These days I usually buy Rich's Brew which I have custom blended by Randy (I live about 10 miles from his hobby shop) and that blend contains both castor and synthetic. Wildcat also works well for me as does Byrons and Powermaster.