Assessing the damage

Yesterday my friend MS and I assessed the damage to the ceiling to the guest bathroom following Septembers episodes of torrential rain. It looks like I will have to replace the sheetrock in the ceiling. But, on closer view of the ceiling, it looks like the leak has been around for quite some time. We poked and prodded the ceiling and discovered a lot of give in the ceiling. MS says the damage to the ceiling is the result of years upon years of leaking. In other words, this problem started before I moved into the house. I am not looking forward to the costs of replacing this sheetrock.