Tim, yes the core inside the plastic housing is the thing that is leaking.
This is very common in Vanagons.  I have new rear heater cores that come with
the seal for the heater valve for $70 each plus shipping.  Let me know if I
can help you.

Thanks,
Ken Wilford
http://www.vanagain.com
John 3:16

New Phone (856)-327-4936
Shop: (856)-765-1583
Fax:     (856)-327-2242

[text/html]