Mold is showing up on floor molding along adjoining wall with next unit. Units are mirror images and black staining is present on both sides of the fire wall. No other signs of water damage except along floor molding, side of vanity has absorbed water and bubbling of linoleum near vanity. Walls and ceilings appear fine. Seepage is worse when neighbors are home. Plumber has been here 3 times no resolution to date . Any ideas would be appreciated .