Do i need a new differential for my losi mini desert buggy?

it makes a loud scratchy rubbing noise and goes nowhere, the gear that the motor is hooked up to spins and looks fine but it goes no where and occasionally catches but then stops and does the same thing. one thing is it catches better when going backwards but u have to ease on the throttle or itll make the same noise and go no where. i took it apart and it appears to be all fine no chipped gears or anything so what might the problem be? also i hit high jumps and what not with it so it has had a beating