See I'm a stickler for making sure its right, if the O' ring didn't work and replacing the piston n barrel still didn't fix the problem then I'd replace the lever. Only because the one time you push yourself will be the one time it fails...not a risk I'm willing to take for the sake of a few quid. Each to their own like and if it works for you then it works for you, but I'd rather have 100% confidence in my brakes. Cause you never know.