Early Focus MK IIs (up until the 55 plate) did not have stone chip protection at the back of the front wheelarch at the end of the sills. Ford’s resolution was to fix a plastic protective strip from this point right to the back of the sills to all Focus II and C-max from 55 onwards.
Ford issued a TSB (Technical Service Bulletin) for those with older cars who went to dealers and complained about rust. They still had to be covered by warranty and / or goodwill (note Ford’s anti-perforation warranty probably doesn’t apply to this as its rust from the outside in. And it seems you have to pay at each service for a bodywork inspection for the anti-perf warranty to be valid). The TSB is 722005 and it involves repairing the paintwork and fixing the same plastic strip used on newer cars
Since pre-55 plate Focuses don’t have the fixing points for the strip, the TSB describes cleaning the surface and using of two part adhesive to hold the strip in place. The plastic strip parts required for an estate are:
wheel arch protector: 1440535 (RHS) 1440536 (LHS)
plastic that runs sill length: 1380593 (RHS) 1380594 (LHS)
The parts might be the same for other focuses / c-max.
I decided I couldn’t be bothered with this potentially un-undoable fix and repaired the paintwork and installed mudflaps which cover, and, I hope will protect the vulnerable paintwork, although I’m not convinced that the paintwork repairs I did will hold for more than a few years.
EDIT: just found this post www.fordownersclub.com/forums/index.php?showtopic=8380 that refers to the problem. It seems that it still occurs even with the plastic strip fitted to 55-plate onward cars. Interesting as well about the cut sponge behind the wheelarch protector, on one side of my car it was cut too, a very clean cut that I assumed was intentional, but thinking about i now was probably damage during installation. When I was wringing it out I noticed that they have small perforations, presumably to make them easier to compress when installing, or to possibly allow any trapped moisture to evaporate.