<<The comment was made that they were not keyed to any specific key.
That is not correct.>>

Steve,

Not to get you all cranked up because you are the key guy here, the man
with the plan, the guru of tumbler's on the Vanagon list.

Allow me to enlighten you.

I've had 5 Vanagons ( 9 if you count junker's) and one key or another
has always fit all.

Ok, and this would go with your spongy tumbler / cap theory.

However, when it was required of me to buy a new cap to pass emissions (
direct from VW parts ) the key in any of the rides, ( or any other VW
key I have for that matter) always fit the new cap.

No gas soaked tumbler / lock this time.
Or 3 other occasions I have bought new caps.
The gas cap's don't even come with a key from VW.

 Can you elaborate on this phenomena?

I'm interested.