Freddie Mac’s top three executives were suddenly replaced this week with officials promoted from within in a major shakeup apparently sparked by shareholder concerns about the company’s drawn-out effort to reaudit financial results dating back three years. Leland Brendsel, who has been Freddie’s top executive since 1984, abruptly retired from his position as chairman and CEO of the GSE, while the board of governors fired David Glenn as president and Vaughan Clarke resigned from