Two (2) to four (4) days before serving, wipe the meat with a damp cloth, then place in a large plastic bag. In a large bowl, thoroughly combine the vinegar, Coca-Cola, water, onions, celery, carrots, pepper, cloves, bay leaves, sugar, and salt and pour over meat. Fasten bag tightly and lay flat in a 13 x 23 cm pan. Refrigerate, turning bag each day. (If you like a sour sauerbraten, let meat marinate 4 days.) When ready to cook, remove meat (saving marinade) and dry well. Rub the surface lightly with flour. In Dutch oven, heat oil or shortening and slowly brown the meat well on all sides. Add 1 cup of the marinade liquid plus some of the vegetables and bay leaves. Cover tightly and simmer on surface heat or in a preheat, 180ºC oven for 3 to 4 hours until the meat is fork-tender. If needed, add more marinade during cooking to keep at least 1 cm liquid in the Dutch oven. Remove the meat and keep warm until ready to slice. Into a large measuring cup, strain the drippings. Add several ice cubes and let stand a few minutes until the fat separates out. Remove fat, then make gravy. TO MAKE THE GRAVY: In the Dutch oven, combine the gravy ingredients, stir and cook about 5 minutes over medium heat until gravy is thickened. Taste for seasonings. Makes 3 cups of gravy. Makes 8 servings.