What a failed window seal looks like
Fog, haze, or moisture between panes usually means the insulated glass seal has failed. That issue affects appearance and efficiency, but it is not always the same as rainwater leaking into the wall.
When exterior repair is involved
If the frame, trim, siding, or sheathing around the window is soft or stained, the project may involve more than glass replacement. The opening may need flashing or siding repairs before it is closed up.
When full replacement makes sense
Full window replacement may be the better value when the unit is old, the frame is damaged, the operation is poor, or siding work is already planned around the opening.
Before pricing the repair, it helps to separate glass failure, frame failure, and exterior water management.