Thinking like a welder. but in miniature..
Dremel a V into the crack and run a tig pass over it, . file the bead down.. though it may likely locally melt some of the brass that was used to build it in the 1st place.
a bulge formed BB should have drawn brass in under that spot.. .. perhaps you can ride with a helmet cam mounted there looking at the site,
and see how much it moves .. as you ride .. maybe live with it as you build another one to replace it.