I recently noticed water in my closet on the back side of my shower.

The leak seems to only occur when the shower is running.

I opened the walls and there was no water coming out anywhere except the very corner. The pipes are all dry.

I had a plumber out and he said there isn't a leak, that the water must be weeping through the grout. He suggested I get someone out to seal all of the grout.

Being a bit skeptical, I put the water hose over the drain and ran a lot of water through, but there was no sign of a leak.

I have now ruled out the drain, the supply and the lines between the supply and the shower head.

My shower is about 8 years old and is sealed granite. Should I have the grout sealed or is this a long-shot?