thanks in advance for getting through the lengthy message but want to include all details...

we recently had some small intermittent leaks in our first floor kitchen - no rhyme or reason as far as timing but we do have bathrooms above (my teenage son's bathroom is closest to leak). i thought maybe driving rain could have been a factor but roofer came out and did not think this was the case and thought it was probably leaking from bathroom above. indeed my son had not been using shower curtain correctly and there was water all of his floor.

so decided to recaulk all of our bathrooms upstairs to make sure all is sealed well etc. and see if if that stops the leak which has not occurred for quite a while even though we are all using upstairs showers continuously.

here is my problem: our freestanding master shower was recaulked and it never would fully dry in places where the wall meets the floor. we thought it was because too much grout had been scraped out in preparation to recaulk so we regrouted the seams where walls meet floor with plans to caulk over that once the grout dried. after days with a fan in the shower there are a few areas that still won't dry so I decided to run a hot hair dryer on those areas and this is where it gets weird. in one area under the shower door, running the hair dryer made other wet areas along that seam pop up and some water drops seeped out of the grout about 4 inches above the seam where I had directed the hair dryer!

clearly there is moisture trapped between the tile and the pan but I am not sure where to go from here. the grout on the shower floor does not appear wet - only see this on the seams. would you first test that the drain weepholes are not clogged (how does one do a test like this?) or would you open up the wall behind the shower plumbing to see if there is a small leak? need an experienced guide to help me so that I will know how to proceed and have the right questions to help me pick the best plumber to diagnose and fix the problem. thanks in advance for any input!