The recommendation was made to use graphite in the locks.  That's the most
common cause of gumming them up. The graphite mixes with the VW grease and
turns to a mud that's quite difficult to remove.  We first solvent clean
then ultrasonic clean them to free them up.
Steve Sandlin, Registered Locksmith
Steve's Lock Shoppe
http://www.steveslockshop.com