"This is a small vial of tiny aluminum flakes"

That would be AlumaSeal.  About $2 and you may need too vials.  I agree
that it works, and have been clogging my leak with it for 60,000 miles.

I have no cooling system problems with it except that it seems to
eventually trash the pressure cap.  It takes about a year but the cap can
be disassembled and cleaned to make it good as new.

Mike

Phoenix, AZ