It's a shame he just missed the forest river FROG factory rally in August. Anybody who camps at that really gets. Hip to give repairs (and often times more) free. A friend has a 2006 cedar creek with a leak in the basement, they replaced the whole section for him. many sidewalls were replaced there too. Lots of work done yo mine but I'm still under warranty.
Unfortunately as stated above, you are SOL here as mold comes from moisture. If that area was moist with mold it is still getting wet. Best way to look for a leak is with soapy water. Look for large bubbles. frequently the source is a marker light or a miniscule crack in the caulking. Forest river is probably saying two things.... 1st you are out of warranty. 2nd, they will likely find some way to blame maintenance. That said, if the leak is from the roof and you can prove adequate maintenance then you might be able to force the issue as the roof has a longer warranty IIRC. Good luck.
