Crushed garlic, and onion and place in a small bowl or mason jar.
Finely chop the parsley and add to the bowl.
Add the Worcestershire sauce, Guinness beer, soy sauce, and seasonings then mix well to combine.
Let stand for 30 minutes to blend flavors. Place the rib eye in a resealable plastic bag and add the marinade.
Make sure steaks are well coated. Seal bag and place into the refrigerator for 2 to 8 hours.
Preheat the grill. Remove steak from bag making sure to reserve marinade. Place steak onto the grill and cook for 6 to 8 minutes per side, or until it has reached the desired doneness.
Add remaining marinade in a small saucepan and simmer sauce over medium-high heat for 5 minutes or until slightly thickened. Make sure to stir often.
Reduce heat to medium or medium-low if necessary. Add more beer to the marinade at this stage if desired.
Once cooked through, remove sauce from heat and let stand until steaks are ready.