1 (28- to 32-oz) can whole tomatoes in purée, coarsely chopped (including purée) in a food processor
2 tablespoons chopped fresh flat-leaf parsley
2 tablespoons chopped fresh cilantro
1 tablespoon Sherry vinegar or red-wine vinegar
Special equipment: an 8- to 9-quart heavy pot
Preheat crock pot on low setting.
Pat oxtails dry and sprinkle with salt and pepper. Heat oil in pot over moderately high heat until hot but not smoking, then brown oxtails in batches without crowding, turning occasionally, about 5 minutes per batch. Transfer as browned to a crock pot. Pour off all but 1 tablespoon fat from pot.
Remove and discard casing from chorizo, then finely chop sausage in food processor.
Cook chorizo, onion, carrots, garlic, and bay leaf in fat in pot over moderate heat, stirring occasionally, until onion is softened, 6 to 7 minutes. Add paprika and cook, stirring, 1 minute. Add wine and bring to a boil, stirring and scraping up any brown bits. Pour into crock pot and add the chopped tomatoes (liquid should come about halfway up sides of meat).
Cover pot and cook 6-8 hours until falling off the bone. Skim fat from sauce, then stir in parsley, cilantro, vinegar, and salt and pepper to taste.