Radiator drain plug problem 98 Lumina

Mother's '98 Lumina, excellent condition, only 21k miles, never had coolant change.
 
Coolant plug at lower left side of radiator looks like a standard plug - plastic butterfly grip for removing by hand. Could not turn by hand.  Tried to gently turn using pliers but only got about a quarter turn before grip started to break off.  Tried moving back and forth a few times but a quarter turn is best I could do.
 
Is there some trick to removing the plug?
 
Thanks,
 
Pete