Using a sharp knife, cut through the joint of each leg quarter to separate into two pieces. Place chicken in a 4-qt. slow cooker., In a small bowl, mix ketchup, orange juice, brown sugar, vinegar, oil, parsley, Worcestershire sauce, garlic salt and pepper; pour over chicken. Cook, covered, on low 5-6 hours or until meat is tender., Remove chicken to a serving platter; keep warm. Skim fat from cooking juices; pour into a measuring cup to measure 2 cups. Transfer to a small saucepan; bring to a boil. In a small bowl, mix cornstarch and water until smooth; stir into cooking juices. Return to a boil, stirring constantly; cook and stir 1-2 minutes or until thickened. Serve with chicken.