It took a contractor to find this tricky leak in Folsom. Others were trying to repair all sorts of likely sources of the leaking water. Plumbers putty, tightening of the drain, and checking the overflow proved to be useless. Sometimes finding the leak is just hard to find.
After all the other ideas were exhausted, I had a chance to take a look. I opened the ceiling below to get a look up close, I could see that water had been leaking for some time. It was hard to see the crack, but I know from experience that this was the reason.
After cutting out the damaged plumbing drain, I could easily prove that this was the source of the water leaking into the unit below. It was a little tricking putting it back together but that's why we get called – we know how to make things rught again.