Just out of curiosity, were the wires connected at the screws or plugged in the back? The reason i ask, if connected at the screws, a loose connections and high humidity could lead to what you photographed. If the wires were plugged in the back, I am not sure of the cause. Also, I do not recall ever seeing a 'outdoor' rated outlet, the cover provides the protection for indoor versus outdoor use.
If you have had your house power washed, I have have personal experience where the 2000 PSI power washers were able to damage electronic (outdoor rated) equipment. These could not handle the high pressure washing but were fine for normal weather conditions. Also, some of the power washers use some chemicals to aid in cleaning the walls, which MIGHT cause the corrosion.
In any glad you replaced the outlet, and double check the weather resistant cover plate and gasket.
__________________
Pennsylvania, for 60+ years, most recently, Allentown, now TV. 
|