1. In a small bowl, combine brown sugar, vinegar, sherry, soy sauce, canola oil, red pepper flakes, paprika, chili powder, Worcestershire, seasoned salt, garlic powder and parsley.
2. Score flank steak on both sides and add to resealable bag with marinade. Refrigerate and marinate 1 to 3 hours.
3. Remove steak from marinade. Grill over medium heat until cooked to desired doneness, preferably no more than medium. (Cooking time will depend on thickness of steak.) Remove steak from grill.
4. Let rest at least 5 minutes, and then slice steak against the grain.