I'd like to answer the poll but there is no option for:
The corrosion was there during the warranty period, but I did not notice it until after the warranty expired, and I have not pushed it with my local dealer because it is only on the bottom, so far.
From what I understand of this problem, it has nothing to do with detergents or salt or anything else. It is 100% manufacturing defect ; caused by iron contamination in the welds of the hood ; and since it is practically impossible to remove that iron contamination, it is practically impossible to "fix" permanently. You can clean up the surface and repaint it, but the contamination is still there inside, and that is why it comes back.
Yes it's a challenge designing the perfect poll. If Ford does fix you up, the last box is for you though! I put the last box in thinking that a lot of ticks there would indicate that Ford realizes there is a legitimate issue.
Thanks for the additional comments, that helps too. The iron contamination theory I've seen mentioned, but I have yet to see the unmistakable red color of iron oxide in these problem areas. It has always been the white powdery form of aluminum oxide.
I think there is no doubt that this is an engineering/manufacturing SNAFU.