Answered: NEC3 ECSS Defect Rectification when the Sub-Contractor doesn't believe it is their responsibility.

The relevant clause is 42.1 and it says "If the Subcontractor has not corrected a notified Defect within its defect correction period, the Contractor assesses the cost of having the Defect corrected by other people and the Subcontractor pays this amount."

I.e. it comes off the retention in your case. So if the retention does not cover it, and they refuse to pay any more, the short answer is 'No'.