Likely it is all title. If the bottom is shower pan it it is dificult to leak.
The worst thing I would do is to cut the grout using 4" hand saw first then grout remover saw and re-grout it. This will be a no more-than-3 hour job for a professional with essential tools. Re-tiling the whole thing is safer but I think it is not neccessary.
I fix the same problem as I described and no leaks ever since.