near toilet floor constantly wet

really old ball and siphon. I'm gradually getting rid of them…

the stack usually goes through the roof near the bathroom so the stack flashing is a common source of leaks in a bathroom

In my 1/2 bath I had an Eljer "Emblem" WC. The one's with the squarish front.

Wet under the bowl, changed the wax and still wet.

There was a silicone caulk plug in a hole that was necessary apparently for the casting of the bowl.

I re-caulked the opening and was good for 2-3 years.

The Eljer then went to the curb and was replaced by an American Standard elongated bowl design…….would never get standard shaped bowl again, the extra bucks are worth it for comfort and targeting.😉

roof leaks can make it to the basement. i'm not saying that is what it is but it certainly is possible, especially if there is a pipe in a chase from the roof for it to follow.

Is the shower in regular use or just idle? If it's in use, avoid using it for a while like @MikeL_2 suggests and see if the water dries up

It would also be worth popping the shower handle escutcheon off and seeing if you can see any visible leaks from the shower handle body

is the stack vent in that wet wall? roof leak coming down the outside of the vent?

If nothing else is found as mentioned. The next thing is to look in the wall.

@pumpcontrolguy makes a very good suggestion. Removing the escutcheon from the shower valve and looking and listening inside the wall is a great idea.

The water could be tracking down from the vent stack or the buildings framing regardless as to how well it may look.

Since the bathroom is not being used as you mention, water can be tracking from a leak other than the fixture where the leak appears. Keep note of when it rains. I had a similar leak that came from outside and was delayed in showing itself. Use a garden hose and spray the suspected area(s) and take note of what happens and or how long the leak reappears.

The leak could also be coming from another bathroom or plumbing fixture and track from there.

I also had a leak occur like this from an over extended drier vent. Water pooled and leaked from the vent pipe. Keep track of when you use the clothes drier.

Good luck. Patients will win the race.

Flat roofs are like swimming pools. The membrane can get damaged and cause all sorts of leaks.

One guy years ago and new to the trade, said he drilled a hole in a flat roof from below and instantly regretted it. Draining the roof into the building was not his intention. Yikes!!

I had a leak that was running down the vent pipe to the first floor, across a joist and leaking out of a door crack. Later on, it moved and leaked out of a baseboard, no traces up higher at all.

After fixing it, it re-appeared 10 years later leaking across the 2nd floor ceiling in a totally new location.

did you remove all the screws or setscrews? a lot of delta products with that style handle have a setscrew in the side somewhere. the cartridge itself is plastic so once all the fasteners are out it should just pull off with some wiggling.

the one in the video has a setscrew

if all the fasteners are out some wiggling and pulling will get it free, metal doesn't seize to plastic.

kroil probably wouldn't be super useful here. The CLR or Vinegar are acidic to help break down calcium or such that has deposited between the handle and the cartridge.

Sometimes you just need a little brute force. A slide hammer puller can be handy for something like this

The electrical in the second to last picture is very rusty. Some water is getting there.

That the flex supply to the toilet has rust spots all over it

can be but must be accessible via removable panel

Is this a screw in the pipe