I took my dashboard fresh air vents out yesterday to see if I could stop the air leakage on mine. Getting them out of the dash, disassembling, cleaning and re-assembly took a little less than a half hour. If you want details for that procedure, please p-mail me and I will write something up. 
After I went through all of that and re-installed them, I found that they still would not close completely without a little help so I ended up doing the following:
Use a light to look inside the vent and operate the lever to close the vent. There should be an oval flap that is controlled by the lever. Stick a regular pencil, erasure end first, through the vent and gently push on the side of the oval flap while pushing the lever to the closed position. You should be able to feel the lever come to a positive stop. Try opening the vent. The lever should have some resistance before it opens the vent. Close it again using the pencil. Test the seal by closing all the heater control vents (Top lever to the right, bottom two levers to the left) and putting the blower fan on high. You should have NO airflow through the vent after you close it.
BTW, I fixed my vent for the opposite reason, to keep hot outside air from coming through the vents making the A/C more effective, but I'm sure none of you up north want to hear about that:>)

Tim
Goldibox - 1987 Wolfsburg Edition Westfalia Camper
Winter Park, Florida
  Fellow Vanagonites,
  Does anyone, have an idea of how to shut down the artic blast coming
  from the cold air vents on the dash of my 85 GL, short of removing the
  grills, and plugging them with foam rubber or something?
  The flow levers are pushed towards the bottom of the dash, but the L/H
  one especially, is causing my left knee cap acute frostbite!
  Any ideas?

  Thanks,

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  Terry 85 GL

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