V6 Mount Shock Absorber - 99 Avalon

99 Toyota Avalon. There is a shock-absorbing mount, mounted between the engine and chassis, to the left of the conventional frount engine mount. How often this needs to be replaced? How do I know if it is bad?

Engine - Mounts - Vibration damper
Or shock-absoring mount
12307-20021
Toyota Part Number: 12307-20021