Looks like some lessons learnt here. If it was me I would challenge the 12 year corrosion policy and claim a design fault of the bodywork to allow crud to collect in this area making it repairable under the warranty. My wife's KA was fixed by Fords after an altercation with another car and the job was 100% top notch.
In that case ford were getting paid for it tho, Checking my service book and theres one missed service stamp and only one body and paint check stamp its probably going to take forever to get them to do it and for the sake of about £30 worth of materials and a lot of my time I am going to attempt it myself.
Ive painted wing mirrors and some engine dressing parts which turned out pretty dam good if I do say so myself in the past lol (and its a bit of extra practice before I get a zetec S kit for xmas )