Don't forget to check to make sure that the head tube isn't where that water was being stored... Some quill headsets will allow rain to slip though around the stem and settle into the frame on top of the lower headset... I have seen it. After you finish the servicing (on a quill), push some grease into the gap between the stem and the headset. The other posters have mentioned the open hex hole in some modern headsets... I would be sure to find a what to block that off.... Maybe a small bolt, like from the rack mount, and a matching washer and put them into place with a bit of silicon caulk (aka clear aquarium glue). On second thought you might want to use a hair dryer to really make sure the head tube is dry and coat the inside with the same silicone before putting it back together.