See image attached.
I've been spending time cleaning up corrosion and repainting + waxing the near-side wheel wheel arches for the past while (now done).
Have come across a fair bit of surface corrosion but nothing too serious. However, this pic is of inside the right-rear wheel arch (and wouldn't be atypical of the type of corrosion I've seen thus far). There are a lot of spot-welded sheet steel sections in the rear wheel arches (and throughout the rear end of the car, really). There's no obvious damage (paint chippings or the like) to this section of steel and this area sits behind the wheel arch liner when the car is together, so I'm thinking that corrosion may be creeping unseen between the various sections of sheet steel (and breaking out sporadically)- particularly at or near where they've been spot-welded together..
Not much can be done about this type of corrosion, I'd have thought. Although, hopefully tackling the exposed surfaces will retard it's progress somewhat.
Cheers,
Karl.