There seems to be some confusion on the water tank keys.  A revised water
tank inlet was installed beginning in about 1988.  It uses a small plastic
key.  This tank cover can be identified by the fact that it is hinged on the
bottom, and by opening it, the cover forms a funnel for filling the tank.
It is the unit that is currently available as a replacement part.
Replacement keys are not available for it, however, one list member
suggested a bent piece of wire to open it.  The earlier Westy's has a
top-hinged water tank cover.  The cap did use a cylinder lock.  There are
multiple keys for this lock, and I've never found a code number for it.  If
the key has been lost, the cover can be removed by taking out the mounting
screws fastening it to the body and removing the fill hose going to the
tank.  Most any good locksmith should be able to generate a key for it.  I
charge $17 retail for this, with a discount to list members.  I would expect
the price to be comparable with most locksmiths.  I hope this clears up the
water tank question.
Steve Sandlin
www.steveslockshop.com
'84 Westy
'79 Transporter
'00 New Beetle