The glass is set into a bead of silicone and then the rubber trim is slipped into the frame.
The silicone at bottom of glass has a gap.....water gets behind the rubber trim, runs down to bottom of frame, leaks in thru gap and onto inside frame sill. It will then pool up and spill over the inside lip of frame and down the wall.
You can try to reseal by squeezing caulking etc into bottom but it didn't work on my two that leaked. (same type of window........narrow/tall fixed glass.
I had to remove the windows, cut the glass free of silicone, clean off the silicone with a remover (silicone solvent), lay a new bead, reset glass then reinstall window
