I had a fixed pella sash replaced yesterday (the pella guy said it needed replaced when he inspected it. He said it was bad on the side) When they removed the sash, the frame on the side has water damage. It was at the bottom right side, but the bottom piece of frame that goes straight across was fine. The area that was wet was between where the sash meets the frame. I asked them if it could have happened because the wiper seal or another seal around the sash failed. Of course they said "no" and it wasn't their sash that failed. He did find some bugs piled behind the wiper shield right in that spot. They installed the new sash and said that it would be sealed very well and if it was the sash that let water between it and the frame that it would stop leaking. In your opinion, what would cause water damage just between the fixed sash and the main window frame? He was telling me it could have come from above the window behind the siding, but the rest of window frame was fine from top to bottom except for that one spot toward the bottom of the right side. I have not seen any water on the floor or wall inside the house. House is on a slab.
I always suspect the installation, as some installers don't get the Window sealed to the house. You're asking me to guess about where your window leaks, which is tough to do and would just be my guess.
If I was there, I'd get my hose and find out where the leak was for sure