i knew i had heard that refrain before:
from Service Bulletins, Model Year 1985
(available from Dyment Publications)
.........................................................................
VW Technical Information
Group 19, Number 87-03
Date: December 21, 1987
Model(s):  Vanagon, Water-cooled, model years 1983-1985
Subject: Carpet wet by rear seat - heat exchanger T-piece leaking

A coolant leak in the rear heat exchanger area may be due to poor hose fit
at the metal T-piece which connects the fee hose to the main coolant hose.
An imporved, white plastic T-piece with slightly larger diameter is available
to correct this condition:
* Replace metal T-piece with white plastic version, Part number 253-265-543A
* Remove flow restrictor from inlet fitting of heater valve.

Production Change:
Improved T-piece installed as of Nov. 1984, VIN 25 FH 037 898.
.......................................................................
and, from the same exciting volume:
.......................................................................
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
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hope it helps.
joel