I finished my large walk-in double shower last year. Today was under the house and noticed there is a leak. Removed some insulation and see that the subfloor around the shower drain is black with moisture. The area around the drain appears to be the only wet area. I really hate to tear up the tile. Any suggestions on what might be causing the problem. My only guess is a bad seal from the PVC liner to the drain. Any chance i can repair this from under the house instead of tearing up tile?