This is the second time making this repair. It gives some warning that it is about to quit on you, when it becomes very difficult to turn and becomes very stiff. Then all of the sudden it won't turn off the water. With some effort and a little bit of luck it might turn off. That is your chance to go get the part and fix it, otherwise the water will keep running until the main water is turned off while you make the trip to the store.
I hope this video is useful for anyone who is new to this type of faucet like I was the first time one of these quit on me.