i had a 81 vw rabbit p/u (westmorland, pa version) and had the smae problem.
well i took out the assembly and then removed the speedo section and found
some of the clear plastic housing inside was cracked and a red gear was
cracked too. i super-glued it back together and it worked. i'm not sure if
the vanagon has the same setup but since VW likes to keep things same for all
it's cars/trucks/vans so i think it will be the same.  if you do decide to
take it apart make sure you mark the speedo needle with it's drive shaft pin
if you pull it off.

good luck

kurt thomas
87 syncro (for sale=2500 obo"military moving forces sale")