The corrosion affecting this early-production 2013 MKZ was along the seams of the hood and doors where seam sealer was used to cover the edge where exterior sheet metal folded over the structural sheet metal. The seam sealer was applied to the bare aluminum prior to painting, and small cracks formed between the seam sealer and the paint, allowing moisture to penetrate. Where this occurred, the seam sealer promoted corrosion of the aluminum hood and door panels rather than preventing it.

The solution was to remove all seam sealer, any corrosion exposed along the seams, and paint the bare aluminum with a high-zinc content marine grade primer sourced from a marine supply store. A color coat was applied next, then new seam sealer was applied, then a final color coat. It's been two years and the corrosion hasn't returned.

I took this to the dealership body shop and the manager checked with Ford and says it is out of warranty so they won't fix it for free. I am going to present him tomorrow with a TSB 16-0028 that I found on somebody's facebook page. That person actually sued the dealership in small claims court and won. Let's see where this goes. I sat in the dealer's showroom two years ago, in March 2015, and wrote out a check for this gently used vehicle! I keep it in a garage and baby it. Now this!!!!! :(

Update from Jun 18, 2017: My update is a positive one. I asked the bodyshop manager for the number for Ford's regional manager. He said he had a number for me to call but couldn't name a manager, to just follow the prompts. He also said he was not allowed to coach me but advised me not to refer to "Ford" but to refer to myself as a Lincoln owner. He also told me that my warranty had expired 42 days before and mentioned that if there were a hole in the hood of my vehicle I would qualify for a penetration or puncture warranty. He also gave me the repair order #. I calmly explained my problem and the man from "Lincoln" said he would get back to me. He then phoned me the next day and said that they would pay $450 toward the $816 repair. He also said that he would talk to the dealership about contributing to the repair cost - which they did; of the $816 I paid $200. While I initially told myself I would sue them in small claims court if this was not a free repair, I was ultimately happy with the outcome.