Theresadang can I suggest that whilst the plumber does a pressure test to check for a leaking pipe please have him also conduct a flood test to the wet area above (all of them isn’t a bad idea). It may be a failure to the water proof membrane within the shower enclosure. When flood testing he just has to make sure the water is from a tap outside of the wet area (shower). Good luck and I hope you find it’s an easy fix as I understand the emotional investment with property
Thanks CBAS, will definitely request this if we end up buying the house and the vendor agrees to fix it...well he's gong to have to fix it regardless if he wants to sell to me or anyone else.