I think what they mean is the drive-shaft splined drive stub/shaft has seized into the drive flange/hub.
This means the whole lot (carrier/hub and drive-shaft has to be removed to the bench .. then freed. Then a replacement outer cv joint if damage caused) This may mean a replacement wheel bearing and maybe even a hub. Best use some heat to get separated) So this could be quite expensive. Maybe as much as £250. Sorry! Al.
It should be normal to replace both gaiters as they deteriorate at the same level. If you had said a nick in the gaiter had been caused by an object allowing the packed grease to escape it would be a different matter.