Not that common unless you don't take care and maintain the slipper and adjust properly. They do wear out over time. But I have never had a slipper problem or have one just break a pad off.sorry that happen. Just make sure that you do mantiance on the truck and keep a eye on the slipper and...
Welcome to the mad house of RC.
With the nitro cars/trucks. There's alot more vibration then in a electric vehicle. The slipper pad could have not got a good seat at factory. Defective maybe. You Could call/email traxxas they might send new one to you. If still under warranty time period...