For the Dumplings:

1. In a bowl, whisk together the eggs and vegetable oil. Stir in the matzo meal, parsley, salt, and pepper. Add 2 tablespoons seltzer water and stir to form a slightly sticky mixture. If it is too dry, add 1-2 tablespoons of seltzer and stir to combine.
2. Cover the bowl with plastic wrap and refrigerate until cold, about 1 hour.
3. While the dumplings are chilling, bring a large pot 3/4 full of salted water to a simmer.
4. Form the chilled matzo mixture into 12 balls that are about 1 inch in diameter.
5. Drop the balls into the simmering water and cook uncovered until they have expanded and are cooked through, about 20-30 minutes. Drain and set aside on a plate.

For the Soup: 

1. In another large pot, simmer the vegetable stock. Add the leeks and carrots. Cook until tender, about 10 minutes. Season with salt and pepper to taste. 
2. Add the matzo balls to the stock to reheat. Ladle the soup into four bowls, placing a few matzo balls in each bowl. Garnish with some dill sprigs in each bowl, and serve.