Sam,

Ken Wilford just fixed this for my newly obtained 88 Wolfsburg.  The
possibilities are:

    1. bad coolant sensor- replace it.
    2. cracked expansion tank-replace it.
    3. (The tricky but actual cause for my leak, which     became obvious
after solutions #1 and #2             failed.)  The o-ring which goes with
the coolant         sensor was the wrong size, so it stretched
too much and didn't seal properly.  New o-ring         and all was fine.

Budd Premack
86 Syncro, 73 Super
Minneapolis, MN (Land of Sky-Blue Waters)