If the owners can prove the tiles had been changed before he bought and the courtyard is common property, then they are the responsibility of the Owners Corporation. If the owner can't prove the tiles were there when he bought or if the courtyard is on his title, (ie, not common property) then it's his problem.
Assuming for a moment that tiles are common property and were there when he bought, I would make two offers – either the OC reinstates the tiles to being the same as the other courtyards or you repair them on condition that he takes responsibility (via a special resolution by-law) for their future maintenance.
This, by the way, is another reason why we should never allow changes to common property to a “nod and a wink”.