MINI Cooper Crank Pulley
The stock MINI Cooper Crank pulley on both the Cooper S and the normal Cooper also serve as a Vibration Damper.  The Crank Pulley itself is what drives the supercharger, water pump, etc. etc.. The Crank Pulley in either model actually has a secondary ring of metal that is connected to it by way of a vulcanized rubber membrane.  The rubber is very scientifically designed to help control the vibrations inherent in all engines today.  The Vibration Damper part of the Crank Pulley is a critical part of maintaining engine life. The problem over time is that it works very hard on the MINI Cooper motors and is also often a point of failure.  The rubber itself degrades with all the heat and the actual controlling of vibration and it in turn fails.  When it does so, it separates from the crank pulley causing a pretty major failure.
Latest Model Factory upgraded original and high performance upgrades are all great alternatives.