On the repairing of a loose rib without removing and re-laying it, I can add what I've learned a little about. First, the loose rib may have left an un-tinned surface that may or may not be corroded.
If you are lucky, it may still be tinned. If it is still tinned, simply wire it back together as you would a completely new soldering, with some rosin flux in the joint, then heat with a torch until a fillet of solder forms.
I see no advantage to introducing a lower temp solder. I used to be concerned about undoing whats left of the original solder joints. No longer. Wiring it all properly is easy enough and assures that you can sleep at night...and heat the barrels without worry of unsoldering the original joints.
From my little knothole, I think it's more likely the surface of one part or the other or maybe both, is likely not suitable to solder without cleaning and tinning. This would prevent a solder bond in that area and prevent a local fix.
