If the gaitor is damaged/split it will leak grease on everything and the inside of the wheel, eventually when the driveshaft sheds all its grease and dries up the cv joint wears. If its just the gaitor kit its about £15 from renault, includes the gaitor, clips and grease.
If the cv joint is worn/knocking when going round corners they may replace the driveshaft, recondition yours or replace the joint with the kit. Im not sure how much that is depending on which option they take.