Review

Fixing/ detecting source of leak/damp internal wall

Part of one of our room's internal dry wall is damp/wet. We have cut out a section of gib - see photos There's an outdoor garden directly against the cladding, directly external to the wet internal wall. Initially thought it might be rising damp from the soil but we noticed just one side of the garden soil is wet and the other side is dry. Could be a slow plumbing leak? We're told there was a historic leak from the ensuite which is off the wall to the left of the wet area . I've attached photos of the internal wall cavity and also the outside garden soil opposite to it.