Heat 1 tablespoon oil in a large skillet over medium-high. Sprinkle brisket evenly with pepper and 3/4 teaspoon salt. Add brisket to skillet; cook until very well browned, about 4 minutes per side. Place bay leaves in bottom of a 5- to 6-quart slow cooker; add Worcestershire sauce and 2 tablespoons water. Add brisket to slow cooker. Separate sweet onion into rings; toss with remaining 2 tablespoons oil. Arrange onion rings over brisket. Cover, and cook on low until brisket is tender, about 8 hours. Meanwhile, bring vinegar, sugar, cloves, 1 teaspoon salt, and remaining 2/3 cup water to a boil in a saucepan over high. Add red onion; remove from heat, and cool to room temperature. Place in a bowl; refrigerate up to 8 hours. Remove brisket from slow cooker; cut across grain into 16 slices. Arrange on a platter. Top with sweet onion mixture and remaining 3/4 teaspoon salt. Drain red onions; discard cloves. Arrange pickled red onions on platter.