I have high moisture levels of 55-78% in my exterior shower wall. This is no plumbing in this wall. The shower deck is recessed 4 inches from slab and built on concrete sub floor. I have checked the attic and there is no signs of leaks. The stucco siding has minimal to no cracks in the area. The whole side of the house has a dry reading on a thermo and probe type moisture meter, except when using a thermo meter that shows moisture in the area of the walk in shower. What can be the problem? Where ro I start trouble shooting to isolate where the moisture is coming from?