Among other things, it could be deteriorated flashing around the vent pipe where it goes through the roof above the bathroom, allowing rain/dew/snowmelt water to run down the exterior of the pipe.

Did the tub have an integral tile flange that the tile lips over? If it didn't, and then was installed for shower use, that could be the problem. Couple that with the grout in the tub shower joint that wasn't removed and then caulked over, that could also be your problem.

Hey guys - thanks for the replys!

So, we just had our roof repaired this last summer. So I'm hoping that it's not a vent pipe issue already, and we've definitely gotten drips when it's been dry for days.

As per a flange... I haven't a clue. Short of pulling tile off the wall, is there a way to tell? Would pulling out all the caulking and grout down to the wall and then refilling with proper caulking solve the issue?

Any more thoughts would be great. Thanks!

The joint between the tile and the tube needs to be filled with caulk, and only caulk.

I just saw a big box tile job that butted the wall tile very tightly to the tub.

The joint should be about as wide as a grout joint to allow the caulk to get in and seal, without leaving a hideous fillet of caulk.

So we're thinking that gutting out everything that's currently there and then re-filling with caulk is an answer? Any thing that I'm missing, as per possible other sources of the water?

Often water leaks are a 'fix and try' type repair.

If there is grout in the tile-tub joint it is had to get a good seal with caulk.

When you remove the caulk and grout that is in that joint you ought to be able to tell a couple of things about the construction of the bath. You should be able to tell if an integral tile flange was used because the tub top should form an "L" behind the tile, and if you dig out everything in that joint, you should be coming in contact with that "L".

If you dig it out, and you cannot see the tub material behind the joint, then your caulk is the only thing holding the direct spray water inside that tub when you shower. That's a pretty important job to just leave to a single bead of poorly done caulk!

That leads to the question was a vapor barrier used behind the cement board (or even did they use cement board!)and to a whole other host of other waterproofing questions that may not have been done correctly. It's a good bet that if they didn't do one thing correctly, they didn't do other things correctly, so you if you don't encounter a tile flange, then you may want to think about other diagnostics here that can determine how well this shower/tub was constructed.

Thanks for the advice/insight. I'll definitely keep those things in mind when I get down and dirty with removing what's there. I'll post my findings. Thanks!

Oh, out of curiosity. Lets assume that there is no flange, vapor barrier or cement board (I truly would not be shocked)... is the solution to simply gut the wall and start fresh? Or what would the solutions be assuming just one of those missing pieces?

Consider this. When searching for the leak, you are moving from place to place. The leak may occur when the tub is filled and the heaviest person in the house is in the tub.