had it happen once but only after the springcup bushing came out causing rollers to wear out extremly fast then breaking a arm , so i'd say check the bushings & rollers if you havn't already. good luck
ya the roller on the arm that broke in toast, is that what caused it to break, ill change all 3 now of course but 1500 km? is that all they last. I know i ride it like it stole, but come on....