I would add if there are any gaps in the soldered seam holding the ribs, flood that area with WD40 so you get no rust occurring between the barrel. My bottom rib has lifted for about 1/4 of an inch near the breeches and that is what I do with my own gun. I would likely put new nipples in, Track of the Wolf has a good selection, if you are unable to find a thread and size match I can put you in touch with a long range muzzle loading shooter in the States who makes custom nipples, he has done several for me.

Cheers

Gordon