I also bought this kit.  $30 seemed somewhat high, but the kit is nice enough
and enough chemical comes with it to run a dozen or so tests.  The chemical
is available separately at NAPA for about $8 a bottle.

Buy one of these.

With the amount of discussion on this list about Vanagon waterboxer head
problems, it is probably a required diagnostic tool.  That said, I have not
had occasion to use this on either of my waterboxers.

Yet.

malcolm