The only way I know of to get the filler apart without the key is to remove
the filler from the body of the van.  The filler hose should be
disconnected, and the lock then removed.  There are 27 different keys that
could have been used for the lock.  There are no code numbers on the lock
from which to generate a key. The code was on the key as shipped from the
factory. I can make replacement keys for the fillers, but I must have the
lock to do so.  I hope this answers your question.
Steve Sandlin
http://www.steveslockshop.com
'84 Wolfsburg Westy
'79 Transporter
'00 New Beetle