I would not of evaporated, unless somewhere for the vapour to get out. Most are sealed units, check around underneath it, might find the filling hole under a label. If not, you could make one, drill a small hole 2.5-3 mm through the base, (out of sight from front, only you know best position, as only you know what it looks like) drain out, catch all the snow, wash out with fresh water, then refill. Could try distilled water, less to cause it to discolour again, bung the hole, or use glue gun or something, ideal things are the bungs you get with inkjet refill kits, and the syringe supplied would help you empty it and refill it, and they usually include the correct size drill for the bung.
SD, January 2012
