jaynews wrote:
Looking for advise on how to resolve this issue. This weekend I had a
strange casement window leak occur, apparently during wind driven rain.
Somehow water appears to have gotten behind the drywall and onto the floor,
causing some damage to start to occur to the wood floor.

snip

Just guessing, but based on what I've seen in construction over the
years, it seems likely that the window was installed with poorly
applied or no flashing. The flanges themselves can withstand a lot of
ordinary rain, but with the wind behind it the rain will be driven past
the flanges and into the wall cavity.
The only way to determine whether this is the problem is to remove the
siding and inspect for proper flashing. If your siding is vinyl, this
is easy to do. Vinyl siding is no great repellant for wind driven rain
due to the way it is designed. The popular pressure washers can easily
duplicate this situation as well. HTH

Joe