I believe that some of the users didn't take off their bands while they are sweating/showering/sleeping and there was build up of grime/dirt/sweat.

My personal practice is to wipe it with a wet tissue every night before I go to sleep and remove the Flex (not applicable for Force users) and wash it down with soap to ensure it's squeaky clean.

Anywho, add me up at adrienmkl@yahoo.com
Our garage sales forum or Machines.