The drywall behind the tiles in my shower is damaged. I am certain this is largely due to from a big gap in the grout close to the tub. Would wetness have spread all the way up the wall just from the gap in the tile? Or should I consider the possiblity there may also be a sewerline leak? The pipes to not appear wet, nor is the drywall to the dining room on the other side of these pipes wet.