Trim fat from steak. Score both sides of steak in a diamond pattern by making shallow diagonal cuts at 1-inch intervals. Place steak in a large resealable plastic bag set in a shallow dish.
Combine oil, vinegar, brown sugar, Worcestershire sauce, garlic, salt, black pepper, and crushed red pepper; pour over steak in bag. Add herb sprigs. Seal bag; turn to coat Marinate in the refrigerator for 2 to 24 hours.
Preheat a charcoal or gas grill with a greased grill rack for direct grilling over medium heat. Remove steak from marinade; transfer marinade to a saucepan. Discard herb sprigs. Grill steak for 12 to 15 minutes for medium-rare (130 degrees), turning once halfway through. Remove from grill and loosely cover with foil; let stand 5 minutes.
Bring marinade to a boil. Stir in butter until melted. Thinly slice steak against the grain and drizzle with cooked marinade. Garnish with oregano leaves, if desired.