If it is due to the construction => need to 搭棚
If it is only due to the 玻璃膠 used for too long time, don't need to 搭棚.
Sometimes it only due to the replace of new air conditioner. They always forget to fill in the 玻璃膠. ....:;pppp: :;pppp:
From my experience, you must tell the tenant first, otherwise he/she may say before was not leaking then will deduct money from your deposit. To avoid any argument, I think you better tell the tenant.