So I tried to insure a 90 Multivan with Esurance...they refused
saying "it's a grey market vehicle because the VIN isn't valid"

Now this is a Multivan originally made for the US market and
originally sold and always registered in the state of California.  I
tried explaining that to Esurance and they were not too receptive,
even after I explained they were happy to insure my 1990 Vanagon
Carat which is essentially the same vehicle without a pop-top.

Somehow US market full Westfalias and Multivans got in the "bad VIN
database" at Esurance.  The database they would use to decline
European market Vanagons/Doka's etc with ZZZ and other non north
american VINS ...

Time for me to look for a better insurance company...one that is
friendly towards all Vanagons...

-Paul