Steven Johnson writes:
> I got that leak in my auxilary heater where the elbow from the
> top hose goes into the core.  I'm not absolutely sure but there's
> a white plug thingy a little smaller than a dime that came off when
> I tried to turn it. :(  Now when I run the engine (actually my wife
> ran it while I looked) this thing pees straight up like a baby boy
> laying on it's back! ;P  Anyway.  What's the likelyhood of just
> getting this plug thing with the seal all buy itself as opposed to
> having to by a whole {aux. heater unit to fix this piece-o-shit 
> weak link?

Straight from one of Joel's Technical Service Bulletins:

........................................................................
VW Technical Information
Group 80, Number 87-01
Date: July 31, 1987
Model(s): Water-cooled Vanagons, 1983-1985
Subject: Carpet wet by rear seat - heat exchanger bleeder screw broken

The plastic bleeder screw for the rear heat exchanger may be broken due to
seal swelling.
* Replace with an improved metal bleeder screw, Part number N 902 061 01.
  and new gasket, Part number 861 819 037.

Production Change:
Metal bleeder screw installed as of:
December 1984, VIN: 25 FM 050 887
..........................................................................

The bleeder screw I replaced was made of white plastic as you described
above which is odd because your '91 should have the metal screw according 
to the bulletin.  Anyway, it solved my leaking auxilary heater problem
although I still smell coolant whenever I run the rear heater which had me
thinking that the core itself may have a tiny leak.  I have since convinced 
myself that the coolant residue left in the fiber floor board is the culprit. 

-- 
   Jerry Huff           Data General       _____     Brick
   Unix Development     RTP, NC 27709     | |_|_\      on       \/
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