Whisk vino seco, 1/4 cup olive oil, and salt together in a large bowl. Add oxtails and mix well to coat. Cover with plastic wrap and marinate in the refrigerator for 12 hours.
Drain oxtails, discarding all but 1/2 cup of the marinade.
Heat 1 tablespoon olive oil in a large pot over medium-high heat and sear oxtails until browned on all sides, about 2 minutes per side. Transfer to a large plate. Heat remaining 1 tablespoon olive oil in the same pot. Saute potatoes, onion, and carrots until onions are translucent, about 5 minutes.
Mash garlic and 1/2 teaspoon salt into a coarse paste in a mortar and pestle. Add garlic paste to the pot; stir until fragrant, about 30 seconds. Stir in green olives, bay leaves, sazon completa, sazon seasoning, and allspice. Pour in reserved marinade, tomato sauce, and chicken broth.
Return oxtails to the pot. Bring to a boil, reduce heat, and simmer, covered, until oxtails are fork tender and falling off the bone, about 4 hours.