In a bowl or small food processor, combine the minced garlic, brown sugar, paprika, salt and pepper. By hand, rub this mixture all over the brisket, wrap tightly in foil or plastic wrap, and refrigerate for at least 6 hours or overnight.
Preheat the oven to 325 degrees F (160 degrees C).
Lightly grease a roasting pan with vegetable oil. Place the brisket in the pan and add the sliced onions. Pour the red wine or other liquid into the roasting pan and cover it very tightly with heavy duty foil (or the lid, if there is one). Place the pan in the oven and roast, undisturbed, for 3 hours. Uncover the pan and continue to roast for an additional hour, basting occasionally with the juices from the pan.
If you want to serve the brisket right away, let it sit at room temperature for about 30 minutes before slicing. Arrange slices on a platter, skim off any fat from the pan juices and spoon some over the meat. Serve the remaining pan juices separately.
f you are cooking this a day ahead of time, let the brisket cool completely, then refrigerate without slicing (it's easier to slice the brisket when it's cold). Skim off any congealed fat from the pan juices, slice the brisket thinly and arrange in the baking pan. Cover tightly with foil and reheat in the pan juices at 350 degrees F (180 degrees C) for about 30 minutes or until heated through.