Yeah, it's the ballast. Remove the ballast from the very bottom of the housing and dry out the plug. The ballast inside is filled with silicone and cannot "corrode", but the ballast can short out from current going through the light for extended periods of time.
Usually the ballasts will be fine once the water is removed from around the plug area.
The water inside the light will just drip down into it via gravity. Really nothing you can do against it if your lights are leaking.
also, here's the ballast if yours is blown:
http://www.ebay.com/itm/Nissan-Muran...-/230538739251