1Rub brisket with a little salt and pepper and brown on both sides in hot oil.
2Place half of onion in bottom of a 6 quart slow cooker. Top with mushrooms. Combine red wine and next four ingredients; stir well. Drizzle with half of red wine mixture; top with brisket. Drizzle with remaining red wine mixture. Cover and cook on HIGH for 1 hour. Reduce to LOW and cook 9 hours.
3Remove meat to serving platter, keeping warm. Remove vegetables with slotted spoon; reserve. Reserve 2 cups of liquid in the slow cooker. Stir together the flour and water; stir into liquid in cooker. Cover and cook on HIGH for 15 to 20 minutes. Add vegetables and adjust seasonings.