preheat oven to 350°. In a large bowl mix egg, bread crumbs, 1/4 cup onion, pepperoncini peppers, Italian seasoning, and the one clove garlic; mix well and add ground beef and sausage; mix gently until combined. Shape mixture into 24 two inch meatballs. Place meatballs in a 15 x 10" baking pan. Bake for 30 minutes; drain well.
Meanwhile in a 4-5 quart slow cooker combine crushed tomatoes, 1/2 cup onion, the vinegar, two cloves garlic, oregano, and crushed red pepper. Add baked meatballs to slow cooker; stir gently to coat.
Cover and cook on low heat setting for four -- six hours or on high heat setting for two -- three hours. Skim fat from sauce before serving. Makes 24 meatballs.