The factory foam hinges on the flaps have been failing on a lot of people causing crashes. The fix is to install "CA" hinges - little strips of fabric that soak up CA glue.
Here's the installation of the flaps on my F4U-1A
February 21, 2013
Note: Please ignore the fact that I had the tail gear reversed! I had inadvertently rotated it 180 degrees. (sheepish grin) It's fixed now! :)