This is another update on the saga of = the rear heater repair. 
 
I installed a new heater valve (old one = was leaking where the on/off lever comes out of the valve), and replaced the round, = flat rubber washer between the valve and the plastic body of the heater = box.  Solved!  No more leak! 
 
About this time I opened the sliding = door.  A ray of sunlight entered the van and shone over the rear heater revealing = a smoke like wisp of water vapor slowly rising up out of the left hole where the = heater motor draws in air.  Alas, I have a pin hole leak in the heater core!
 
Has anyone had any luck adding one of = those miracle additives to the water in an 84 vanagon?  Is it safe to use?  = Will it work, or should I just bite the bullet and buy another = core?
 
Any help will be = appreciated.
George
Columbus, GA