In a message dated 96-10-24 00:54:11 EDT, TStone8359@aol.com writes:

<< 
 A Rabbit heater core can be used in a pinch.  Requires some clearancing of
 the shrouding around the heat exchanger to make it fit.  You lose the
ability
 to turn it off in the summer, unless you add in a Rabbit heater valve in one
 of the water lines.  On the plus side, you get to keep most of the $140 that
 the dealer wants for a new one and the $70 that most junkyards are asking
for
 used ones.
  >>

Believe it or not, I have been able to get the rear heater cores aftermarket.
 Cost is still high at around $100.00.  Front cores still not available to my
knowledge.  You could try fitting with VW to get them to repalce it if you
have all documentation for maintenance of the van.

Dennis