It looks like the Sox are taking a depth approach to replacing Billy Wagner and Takashi Saito, as they signed yet another reliever in LHP Fabio Castro.
Castro, 24, has a 3.30 ERA over 43.2 innings with the Rangers and Phillies, last pitching in the majors in 2007. Last year, in AAA, Castro managed only a 4.49 ERA with mediocre peripherals. While Castro has made all but 1 major league appearance out of the bullpen, he's spent his last few years starting in the minors.
Castro is likely to join a large group of pitchers trying for a spot in the Sox bullpen in spring training, including Scott Atchison, Robert Manuel, and Dustin RIchardson.