You have a leak that is not necesarilly on the window area, take a small hammer and lightlly tap on a wall that is not affected to learn the sound, then tap lightly arround the area that is going bad and you will hear how far the problem area extends.
Wet soaked wood or compressed wood sounds dull instead of resonating with a high tone as in dry wood.
Also check arround the air conditioner and all the vents, also on the corners where the front and or rear cap meets the rubber membrane, a leak can be further away than where the damage is located, if the unit has any tilt, even slight the water or moisture will travel to the lowest point until it meets a barrier like a window frame.
That needs a repair and to locate the sourse of the water entry, do not foget to check the marker lights they are also a source of water entry with time the plastic covers crack and allow water to penetrate.
Hope it helps a little and good luck
navegator