Clark County officials say truck-maker Navistar International will add 300 jobs at its Springfield plant and build a second assembly line to boost production. The company will also get a 6-year, 60-percent state tax break to invest more than ten-million-dollars in the factory. Navistar reports a 21 million dollar loss in the quarter than ended on July 31. It is not clear when the investments will be made and when the workers will be hired.