I have also stopped mining with my small rig week ago, and today I wanted to clean and prepare them for selling (1070/1080TI AIB models), But I found big problem! somehow the Aluminium Heatsinks started to build white corrosion right under the fans, they were fine when worked week ago - but now I don't know what cause it and how to remove it- Any Help?
I suppose you live near the sea and the high humidity and salt in the air caused it. While the cards were working the heat protected them from moisture. You could try a high quality wd 40 anti corrosion spray. Its not electrically conductive so your cards should be ok. Dont buy that cheap Chinese stuff.