Aha! Just as I thought! Another closet BL user!

Again: who cares, really, if the leak is stopped by a liquid product that
becomes solid inside the engine, or a solid product that was once liquid
that you have to tear the engine apart to install? The point is, you want to
stop coolant leaks and maintain compression. Whatever gets the job done.

I'm using the Bar's Leak head gasket repair product, 20 oz size--the kind
you have to remove all the coolant to use. Yikes. That's the hard part.

BTW, I just got off the phone with Clay at Bar's Leak central command.  He
told me that you can have up to 10% coolant left in the system and not
create blockages. Lab testing showed problems starting at around 15-20% coolant.