Start testing using a garden hose.
Start with water only along the bottom edge of the window, lower window seal to body.
Use wide painters tape to keep water out of window channels.
If no drips inside after 10 minutes, remove the tape and do the lower window channel and drain area, slow the water flow to not overwhelm the window frame drains, and run under the window and over the frame inside.
Again if no leaks
, move up the water to the upper window seal to body.
You could also try a painters tape seal, roof, over any of the seams and see if the leak is gone in the area
Eliminating as you go is the only way to isolate the leak, or do as I do, pull the window, clean all of the channels and drains, reseal to the body and reinstall