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