04,b2300 antivibration doughnut?

[ursus]

What is this part called? Its the rubber lined circular metal thing that goes around the front driveshaft by the universal joint. Mine fell off and I had a mechanic remove it. Do I need to replace it? I don't notice any problems with sound or vibration since the part fell off. Is it worth replacing?
thanks

 

[martin]

It's a harmonic damper, If you don't feel any vibrations just forget it.