In a large resealable plastic bag, combine the Worcestershire sauce, chili powder, bay leaves, garlic, celery salt, pepper and liquid smoke if desired. Cut brisket in half; add both to bag. Seal bag and turn to coat. Refrigerate overnight.
Transfer beef to a 5 to 6 qt. slow cooker; add broth. Cover and cook on low for 6 to 8 hours or until tender.
In a small saucepan, saute onion in oil until tender. Add garlic; cook 1 minute longer. Stir in the remaining ingredients; heat through.
Remove brisket from the slow cooker; discard bay leaves. Place 1 cup cooking juices in a measuring cup; skim fat. Add to the barbecue sauce. Discard remaining juices.
Return brisket to the slow cooker; top with sauce mixture. Cover and cook on high for 30 minutes to allow flavors to blend. Thinly slice across the grain; serve with sauce.