Stir the broth, oil, seasoning, vinegar and garlic in a 2-quart shallow, nonmetallic dish or resealable gallon-size plastic bag.
Add the steak and turn it over to coat with the marinade. Cover the dish or seal the plastic bag and refrigerate it for 8 hours, turning the steak over a few times while it's marinating.
Lightly oil the grill rack and heat the grill to medium.
Remove the steak from the marinade and pour the marinade in a 1-quart saucepan.
Heat the marinade over medium-high heat to a boil. Reduce the heat to low. Cook for 10 minutes. Stir in the lemon juice and cilantro. Keep warm.
Grill the steak for 28 minutes for medium-rare or to desired doneness.