SIXTO RODRIGUEZ, THE Detroit musician and composer whose work became wildly popular — completely unknown to him — in 1970s South Africa, has died at age 81. The nearly incredible story of his obscurity and rediscovery, years after lurid and unfounded accounts of his death circulated among his South African fandom, was told in the documentary “Searching for Sugarman.” Bryan D. Palmer wrote a moving review essay on Sixto Rodriguez and the documentary in a previous Against the Current.