Place potatoes and carrots in a 6-qt. slow cooker. Sprinkle flour over all surfaces of roast. In a large skillet, heat oil over medium-high heat. Brown roast on all sides. Place over vegetables., Add mushrooms, celery, onion, olives and 1/4 cup parsley to slow cooker. In a small bowl, mix remaining ingredients; pour over top., Cook, covered, on low until meat and vegetables are tender, 8-10 hours. Remove beef. Stir remaining parsley into vegetables. Serve beef with vegetables.