Slow Cooker Garlic Butter Sliced Beef Brisket

3 lb (1.4 kg) beef brisket6 tablespoons unsalted butter, melted6 cloves garlic, minced1 teaspoon salt1 teaspoon black pepper1 teaspoon smoked paprika1 teaspoon onion powder1 teaspoon Italian seasoning½ teaspoon dried thyme½ teaspoon crushed red pepper flakes, optional1 cup beef broth1 tablespoon Worcestershire sauce1 tablespoon olive oil, for searing2 tablespoons fresh parsley, chopped1 tablespoon fresh rosemary, chopped, optionalFor serving:Extra melted garlic butterFresh chopped parsleyBlack pepper, to taste