Heat the olive oil in a large frypan over medium heat. Cook and stir the Italian sausage meat until browned, about 10 minutes. Break the meat up into crumbles as it cooks. Stir in the onion, celery and garlic; cook and stir until the onion is translucent, about 8 more minutes. Pour the mixture into a slow cooker. Pour red wine into the frypan, and stir to dissolve the brown flavour bits from the bottom of the frypan. Pour the wine into the slow cooker. Add the diced tomatoes, tomato sauce and salt to taste. Mix well.
Cover the slow cooker, set to Low, and cook for 5 hours. Pour in the cream, stir, cover and cook for 1 more hour. Adjust salt again if necessary, and serve.