Brown ground beef in 2 tablespoon hot oil in frying pan. When almost browned, add onion and continue browning until onion is tender. Pour meat and onion into 3 1/2 quart crockpot. Add puree, sauce, paste, water, salt, pepper and oregano and set dial on low setting. Cut 2 lbs. sausage into pieces and brown in remaining 2 tablespoons oil. When brown, place sausages in sauce in crockpot. Continue cooking for 12 hours. (If you like your sauce sweeter, you could add 1/4 to 1/2 cup sugar to this.)