Preheat oven to 300 degrees F.
In a large plastic bag add Worcestershire sauce, oils, dry hot mustard, salt, peppercorns and garlic. Mix and add brisket then seal making sure marinade covers all parts of the meat. Marinate for 2 hours. In a Dutch oven or roasting pan place 3 of the onion rings in a circle to form a trivet for the brisket (if using a roasting pan place all onion rings out in a single layer). Place the garlic in the spaces not occupied by the rings, then add one slab of brisket making sure to place it evenly on top of the rings. Add another layer of onion rings then the second slab of brisket (if using roasting pan, place brisket side by side in single layer on top of onons). Pour over the remaining marinade, the broth and wine in equal parts until the meat is just covered. Cover and cook for 3 hours adding the carrots and celery 30 minutes before the end of cooking. Check the brisket a few times while cooking and add salt, as needed, and broth and wine in equal parts if the level of the liquid falls below the meat. The brisket is done when it is tender to the fork and easy to pull apart.