Heat 1 tablespoon olive oil in a large pan over medium-high heat. Sear the roast beef on all sides until browned, about 8 minutes total.
Place the sliced carrots, chopped onions, sliced celery, and garlic pieces in the crockpot. Place the seared roast on top. Pour the red wine and beef stock over it. Close the crockpot.
Cook on high for 1 hour. Then cook on low for 6 to 8 hours. If the low setting feels like a warming mode, use medium instead. Alternatively, use the automatic setting.
Remove the roast and vegetables and place on a plate. Keep warm in a 100°C (212°F) oven using only bottom heat.
Strain the cooking liquid through a sieve into a saucepan. Add roughly a tablespoon of dark sauce thickener and stir until smooth. Season generously with salt, pepper, and paprika powder.
Puree the sauce if desired. Serve the roast and vegetables with the sauce.