Place flour in a shallow bowl; press meat into the flour to coat and shake off the excess flour. Heat vegetable oil in a large skillet over medium; cook and stir meat until browned on all sides, about 5 minutes. Transfer meat to a large slow cooker. Pour beef stock over meat in slow cooker; add potatoes, carrots, celery, onion, diced tomatoes with juice, oregano, Worcestershire sauce, thyme, garlic, and bay leaves. Gently stir mixture Cook on Low for 8 hours. The stew can also be cooked on the stove in a Dutch oven.