I have a question please.
If I understand your post, you have water coming out between the baseboard and the floor of a wall close to your toilet.
How do you know where the water is coming from? How could you, the plumbers, or any one else know that it is coming from underneath the floor. It could be coming from underneath the floor or it could be coming from a leak in the wall.
I would take a hammer and knock a hole in the wall above the place where you first see the water and look.
The problem could be a simple as a leaking solder joint or a pin hole leak. My guess would be that it is a pin hole leak in the pipe in the wall.
I must really be misunderstanding your post. In my opinion, the way you describe how the water appears, it is more likely that it is a leak in the wall than a leak underneath the slab. Right now neither you, the plumbers, nor I could possibly know where the leak is occurring. You only know where you see the water. Sounds like you are about to do a $2500 plumbing repair to avoid a $25 drywall patch job.
Furthermore, if you don't confirm that it is coming up from underneath the slab and not from within the wall, you will never be able to force the condo association to accept responsibly.