Let me guess, the valve retainers failed? It's not the first time i've read about this. After an over rev *unless it's major* the motor may actually drive fine. The damage has already been done however. The retainers are stretched and will crack and fail down the road. No way to tell when, it's a ticking time bomb. The guy that over revved the car could go and sell it and a thousand or ten thousand miles down the road the new owner gets the tab. The AP2 retainers aren't as susceptible to this phenomenon.