Remove the stems, seeds, and membranes from the ancho chiles and guajillo chiles, then soak in hot water until softened, about 20 minutes.
Meanwhile, bring a pot of water to a boil. Remove the stems from the tomatoes, then cut a shallow X on the bottom. Drop the tomatoes into the water, and cook uncovered until the skin begins to peel off, about 30 seconds. Drain in a colander, then immediately immerse in ice water for several minutes until cold to stop the cooking process. Once the tomatoes are cold, peel the skin off. Drain chiles and transfer to a blender along with the peeled tomatoes, garlic, onion, and chicken broth. Blend until smooth.
Heat 1/2 of the corn oil in a saucepan over medium heat. Stir in the chile mixture, then reduce heat to low and simmer for 10 minutes. Season with salt. Heat the remaining corn oil in a large skillet over medium-high heat. Brown the chicken legs in 2 batches and remove from the skillet.
Stir the chorizo into the same skillet; cook and stir until the chorizo is evenly browned. Drain any excess oil and stir in 1 cup of the chile sauce. Return the chicken to the skillet, along with the remaining chile sauce. Bring to a simmer and continue cooking until chicken is tender, 1 hour to 1 hour and 15 minutes.