Brazing actually incorporates the filler metal into the steel for some distance, so you probably need to cut out maybe 1/16" either side of the crack to be sure you get the brazing filler out. Welding will vaporize the remaining brass filler metal, but will also contaminate the weld. The location of your cracks will dictate how thorough you need to be. Can you post pictures of what you need to repair?
