The folks at Rocky Mountain Westy have figured it out, but it'll cost ya!
http://www.rockymountainwesty.com/Vanagon_Aluminum_Expansion_Tank_p/02512140
3-al.htm

I do applaud them for this though.

Stuart

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Larry Alofs
Sent: Thursday, September 26, 2013 8:27 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Expansion Tank Defect

I recently spent some time browsing at the local pick-n-pull, hoping to find
a tank on some other vehicle that could be substituted for the vanagon
pressure tank.  Ideally it would be functionally the same, except having a
"real radiator cap".  I did not find such a tank yet.  I did find some
radiators with long necks that could be cut off and they had traditional
metal caps with provision for pressure bleeding and draw back upon cooling.
 The problem would be grafting such a neck onto our tanks.
  Of course I know there are those among us who believe that the VW
engineers were much smarter than we are and we shouldn't tamper with the OEM
design.  I just thought that I would throw the idea out there.
  Over in the world of Jeep Cherokees there are those who solved a similar
problem using a substitute from a GM product.

Larry A.

On Thu, Sep 26, 2013 at 8:00 PM, WILLIAM WITZ <pbwitz@sbcglobal.net> wrote:

> Hi  all, just a heads up to let you know that I had to wrap a bunch of
> Teflon tape on my new Expansion tank threads in order to get the Cap
> to seal on the tank .  The cap was new as well . Very poor fit on the
threads.
> I ran it on the driveway until the Radiator fan came on. The threads
> then sealed as they should. We got our Westy back after a manual trans
> rebuild, it is now a joy to drive.
> Bill Witz 84 Westy Tiico P.S. we are going bird watching on Friday
> although it may be to early.
>