Season roast with salt and pepper. Heat oil in a large skillet or pot over medium-high heat. When pan is hot, add seasoned rump roast and cook, turning, until browned on all sides, about 1 1/2 minutes per side. Transfer roast to slow cooker.

Pour red wine into skillet and, using a wooden spoon, scrape bottom of pan to incorporate all browned bits of meat. Cook for 2 minutes to reduce liquid. Pour liquid over meat.

Add onion, broth and onion soup mix to pot; stir to mix. Cover and cook on low heat for 5 hours. Remove roast and slice.

Arrange meat on a platter and pour onion sauce over meat. Cut 4-inch lengths from bread, split lengthwise and toast for sandwiches. Have everyone layer meat on bread, pouring sauce on top to moisten.