Listmember Alex had some great advice here.  So today, I tried it.  Called my nearest Autozone, asked if they had the Pressure Test kit for finding leaks in automotive coolant systems.  They did.  Headed over.  Basically, you "buy" a used kit in this case $249.99 but then can use it and return it within 90 days for a full refund on your credit card.  

The kit has a myriad of fittings to connect to radiators of all breeds, or in my Vanagon case the coolant pressure bottle.  Easy peasy.  An air pump (with release valve) is included.  I didn't quite know what pressure to pump it up to....I used 10 PSI to start with...since most radiator caps let go at 15 PSI.
Pumped up....waited about 10 minutes....sure enough...started losing pressure.  Some flashlight work and crawling around....Hey...there is the leak!
The beauty of this kit is that you are inducing leaks with cold coolant.  Minor hot coolant leaks just steams away...you'll never see it, just as Alex describes.  Your nose is a good detective tool as well....smelling something sweet.
So I will fix Leak Number 1, and then try again.  For me as a hack mechanic, this system is a miracle!  And kudos to Autozone.  And Alex.

Rich
San Diego

    On Monday, May 18, 2020, 2:31:58 PM PDT, Alex MeVay <alex@mevay.org> wrote:  
 
 Just wanted to share a tip for tracking slow coolant leaks...  Often,
the heat from running the van will evaporate small leaks without a
trace, but if you get a cooling system pressure test kit (Autozone
loan-a-tool, etc.), you can keep the system pressurized while cold
(say for a few hours), and those small leaks will stay visible.

-Alex (who sees some stainless cooling tubes and an upgrade to a
late-model radiator in his future)