Mixer shower slow leak - next steps?

sapper

Hi noticed a very wet ceiling under my ensuite shower which drips slowly when the shower runs. The shower is about 20 years old and is on a stud wall which I have been able to access from behind to find this (see pic below). You can see the plasterboard is soaked beneath. No visible drips so the water is just soaking into the plasterboard . Its screwed into those T&G boards going across and zero access really between the boards and the tiled wall, so I think it would be a pain to get at the shower valve even from behind (plasterboard is mush in parts)

We're hoping to completely re-do the bathroom in the next year or two (but not right now) so hoping for a low-impact short term fix. Maybe this is a standard problem for a shower this old that a plumber could sort for me? Or will this need the tiles coming off, shower completely removed etc ?

Just wondering what next steps should be really....

Sleeper12

Very difficult to see anything in the photo.

If it only leaks when the shower is running then it's not likely to be the shower itself. There is water in the pipes with the shower on or off. It should be leaking 24/7 if it's the shower leaking.

It's much more likely to be the tiles /grout leaking if it only leaks when the shower is running

sapper

Yeah I did think that myself so I’ve spent the last few weekend checking the joints in the shower and redoing the silicone to no avail. The sink is nearby so I ran the shower into that and the leak started. When I ran the shower with the shower head removed toward different corners of the shower cabinet there was no leak so that and the fact that the wall under the shower unit is soaked but the wall above and either side is dry makes me think it’s a valve or something. I was hoping it’s a standard problem in showers that old that people might have seen before….

It’s definitely not the joints though unfortunately. I could have sorted that…Going forward myself blindly now could cause damage though….