If you have a 2wd Vanagon this is a not that expensive thing to fix.  Just
order a new upper- $12 and lower- $24 Thermostat housing from me.  Might as
well replace the thermostat- $14 and o-ring at the same time.  The only other
thing that could be leaking there would be one of the smaller o-rings for a
sender.  I have these for $.25 each if you just needed that.  Let me know if
I can help you.

PS Syncro Vanagons have a metal lower thermostat housing that is MUCH more
expensive.

Thanks,
Ken Wilford
John 3:16
www.vanagain.com
Phone: (856)-765-1583
Fax: (856)-327-2242