Heat the oil in a large skillet set over medium-high heat. Season the beef with salt and pepper and sear on all sides. Set the seared beef in your slow cooker. Add the remaining ingredients, except buns, to the skillet and while stirring, bring to a simmer. Pour this mixture over the beef in the slow cooker. Cover and cook on the low setting for 8 hours. Use two forks to pull the meat into thick shreds. Pile the saucy meat into the buns and serve.
Note: This recipe is designed for an oval-shaped slow cooker with a 5 litre or more capacity.