I have noticed lubricant leaking from a seal. What is happening?

If the seal has been in service for an extended period of time, it may simply be worn out.  Seals are sacrificial components in most machinery designs, and they are intended to be replaced periodically.  If the seal is in new equipment or has been replaced recently, the seal may have been installed improperly, or there may be a compatibility issue between the seal material and the grease. For example, if lubricating fluid (oil) in grease shrinks a seal, then it may leak.