Looking for advice for ceiling repair

[Anthony Barbato]

I acquired a new duplex back in March and just had the second tenant move in last week. 

When I purchased the property, there was a small amount of pervious water damage to the ceiling in the kitchen, directly under the bathroom. I flushed the toilet multiple times, ran the water in the sink and tub, and everything seems dry, so I assumed it was an old leak that had been repaired. I went ahead with the minor rehab to the unit and moves the new tenants in. They questioned the spot on the ceiling, and I assured them that we looked at it and it was all old damage. 

Well of course (Murphy's Law), their second day in the apartment, I get an email stating that there is water coming from under the toilet and not a fresh water spot on the kitchen ceiling. I hate having issues so early on, I feel as though I lose all credibility and I leave a bad taste in the tenants mouth for the duration of the lease. 

I went ahead and replaced the wax ring on the toilet, which stopped the leak, but now I have the ceiling to worry about. I want to replace the "tiles" or whatever they are, but I'm not sure how to go about doing so. I am very familiar with normal ceiling tiles and grid (drop-ceiling) but these are different and I have never come across these before. I don't know how to find out what these tiles are, and if I am able to still get them. I would take to have to remove all of them and install a new drop-ceiling.

Can anyone give me any advise or opinions on how to proceed from here?