Prepare the beef: cut off any large, fatty membranes. Place the beef in a resealable bag and add salt and pepper to taste, garlic and Worcestershire sauce. Seal and squish around to combine. Place in the refrigerator to marinate at least 1 hour and up to overnight. When ready to cook, remove meat from marinade. Transfer the remains of the marinade into the slow cooker. Heat the oil in a large heavy-based pan over high heat. When the oil starts to heat, add the sugar in the center of the pan and let it dissolve without stirring. Sear the beef on each side until nicely browned. Transfer beef to the slow cooker. Add onions, carrots, green pepper, oregano, bay leaves, beef stock, beef bouillon, and wines to the slow cooker. Cook on high for 4 hours or low for 8 hours. Open the slow cooker and remove the beef. Discard the oregano sprig and bay leaves. Let the meat rest for 5 minutes and then place roast on cutting board and slice into 1/2-inch-thick pieces. Set aside. Transfer the liquid and veggies to the blender and puree into a smooth sauce – it will change from a dark brown to a lighter brown color. Pour the sauce into a saucepan and bring to simmer over medium heat. Add the papelon (brown sugar cane), mix well and simmer until the sauce turns a darker brown color and reduces to a gravy consistency, about 8 to 10 minutes. Taste and adjust the seasoning (salt and pepper) if necessary. Add the sliced meat and simmer for 10 to 15 more minutes. Serve hot with mash potatoes or white rice.