CW is right of course, soldering will bubble the paint. But since all you have to do is tack it in place, sometimes a tiny burnt spot or two is acceptable, especially if there are already imperfections in the old finish. The two sides of the seam are already tinned with the old solder, so it is possible to do it applying the soldering iron from the inside so the repair is not a big blemish.
On the other hand, I got a Richart Olympian that had a similar split in the soldered seam, but the paint was like new and I didn't want to risk it. A thin line of JB Weld applied along the seam with a toothpick and then clamped overnight seems to have solved the issue nicely without damaging the paint.
david
