I dont think I would be going that far. I might still have some lead solder around somewhere if I really look for it. You cant even buy this stuff at the stores here anymore, I would need to do an online search to find some. Its all Tin/Antimony / low lead content. I asked the electricians at work what they thought and they said they would have just dropped a bead of solder in that crack - but I'm thinking, better to replace it with a solid wire and make adjustments to relieve the expansion stress.To completely prevent that, make an S-bend; you may have to cut out some plastic, but if it can move a little it won't fail.
Hit all the punchdown joints with lead solder, make sure it wets, and they are permanent too.
Lead solder, 60/40, has the most give.