Thanks for the help.I'm soaking the joint in some diluted pool acid
In looking thru my toolbox I have a jar of NOKORODE paste flux. Does that sound appropriate for bronze rod? It's very dark brown.almost black in color. I seem to recall the bronze flux was white.
I took a closer look at the other dropout and found Bondo underneath the paint at the dropout chain stay junction !! Hiding the failure to properly fill the joint. I'm thinking this was a high school shop project.