The comment was made that they were not keyed tio any specific key.  That is
not correct.  There are multiple key possibilities.  What we've found,
though, is that almost all the locks have severe grooves worn in the plastic
housing that forms the outer cylinder of the lock, allowing most anything to
turn the lock.  We've keyed up numerous replacement caps, and they are
certainly keyed for a specific key.  It's just a theory, but I wonder if the
fumes from the fuel have softened the plastic a bit over the years allowing
the grooves to be worn in the housing.  I took the cap apart on my own '84
and found wear, but it is definitely keyed up for the correct key.
Steve Sandlin, Registered Locksmith
Steve's Lock Shoppe
http://www.steveslockshop.com
'84 Wolfsburg Westy
'79 Transporter
'00 New Beetle