Use silicone-based caulk to reseal the seam along the roof or replace the entire roof to fix the leak. Squeeze the caulk through a caulk gun generously along the seam. Wipe off the excess caulk.
Reseal the toilet and tighten the toilet if the leak is in the bathroom. Use caulk in a caulking gun around the base of the toilet. It isn't always an external leak that causes the problem. You can troubleshoot the leak to the bathroom if it is damp and smelly, there may also be puddles on the floor.
Check the sealing on shower. Loose sealant can also cause leaks and water damage.
Remove all damaged paneling and the insulation behind it using a hammer and screwdrivers.
Dry off the exterior wall from the inside. You can use a hairdryer.
Sanitize the area with bleach water to kill any mold or mildew. Install the new insulation and replace the paneling molding.
