In a bowl whisk together the beer, 3 tablespoons of the maple syrup, vinegar, mustard, rosemary, oregano, garlic, 1/4 teaspoon of the salt and the pepper. Transfer mixture to a large baggie or marinating dish - add chicken. Turn to coat and refrigerate for 4 hours or overnight.
Spray grill rack with Pam and preheat grill to medium or prepare a medium fire in a charcoal grill.
Drain chicken and discard marinade.
Place chicken on grill, covered and turning occasionally for 30-40 minutes.
10 minutes before chicken is done, brush the chicken with the remaining maple syrup (2 T), turning frequently until chicken is browned and cooked through.
Transfer to a platter and sprinkle with remaining salt (1/4 t).