The lower control arm has to be replaced in it's entirely if the inboard pivot bushings are worn out or if the balljoint has become worn or damaged or if the balljoint seal has blown. New bushings can be fitted to the upper control arm but here one will require the services of the press and special tools hence it is advisable to consult your Ford dealer. The balljoint seal replaced can be fitted to the upper control arm once the arm in question had been removed. As for the wear in the balljoint itself, this cannot be fixed without changing the control arm utterly.