I gotta weigh in here. Just take a fine file and shape the brass down to the metal. After that some 80 grit garnet to remove any file marks you might leave.

Somebody did a poor repair job. Half of the bike boom Raleigh's I've worked on have cracks on the seat stay caps. The proper way to fix those is to take a hacksaw blade and carefully clean out the crack until you get to base metal then silver braze and fill the crack. It's a 5 minute job. What somebody did here is slap some brass on the surface. Maybe it penetrated the crack, maybe not, but at any rate, it's cosmetic. All of the structural strength is between the tube and the seat lug. There's usually crappy workmanship there as well, but somehow they don't fall apart.