Snip !! 
> 
> If coolant is spewing from the coolant reservoir or overflow tank, you may 
> have a crack in the plastic or a bad pressure cap. Exactly where is it 
> leaking?
> 
> -Mark McCulley
> 
 Thanks Mark, 
As Joel had mentioned in previous post, I think its not simply the
coolant reservoir leaking. I believe its  combustion gas leaking into
the cooling system. This occurs only when you push the engine hard e.g.
over 70 Mph. The extreme pressure pushes the coolant out from the filling
container behind the license plate. This will occur when you stop and
switch off the engine.
There are so many prior posts on this subject that I can guarantee that
most Vanagon owners will experience this problem sooner or later.
I also saw a previous post about a lawsuit between VW and Subaru
concerning a design flaw concrning this defect but could not get enough 
details on this. Perhaps someone can elaborate on this.