You don't want brass. You want steel. And personally, since I'm kinda weird about things being symmetrical, I would sleeve both sides even if the other doesn't need it. You will, of course, need to remove all paint within 4-6" of the area to be brazed, and clean properly with abrasive cloth. Sounds like you have a 14mm stay, a scrap of 16mm stay might do the trick for you as a sleeve, depending upon the wall thickness, or just figure out where on a tapered stay you would need to cut to make a sleeve.

Pete