Jim, without knowing the year of your van, I'm not certain the following will 
help. 

I mechanic for 2 '91 GL's, mine and my daughter's. Hers had a leak in the rear 
heater. After taking it apart we discovered that it is a genuine piece of junk. 
i.e. it is of French origin and plastics are used extensively where they should 
not be used.

My tall daughter got on the phone and gently raised hell about the rotten design
of the heater and VW replaced it at N/C.

After looking at the heater, I suspect that you will have a terrible time 
getting it to hold regardless of what you do, if the design is like mine.

Is this heater problem a common one for other '90 or so vans or did we happen to
get a special?

(BTW, Jim, I live in Ames during my real like altho I work at the U of M.)

Herb

Herb Harmison, Placement Director
Institute of Technnology
University of Minnesota
50 Lind Hall  207 Church St. SE
Minneapolis, MN 55455