Hi Lee,
That's what exactly I thought and wanted to do too, to replace the broken part with a new rectangular patch piece. But My Owner insisting me on replacing the entire door and since it is Fire Rated, they said it would cost around S$1.5K. I seriously regret for not bringing Lock Smith or not making a nice move. May be my bad time. Though My Owner hadn't make a visit, their agent came along with a freelancer, and they suggested to replace the door, may be from their word my owner also insisting for the same. I will hear from my agent by next week. let's see.
Thanks for your suggestion.