Hi Adrian. I had the exact same problem with the corrosion, less the leaking air though. My b max was just under 3 years old when I noticed 2 of them and upon presenting it back to my supplying Ford dealer they were very quick in replacing the 2 wheels in question. The other 2 have now started showing small signs of corrosion, but it now been out of it's 3 year warranty, I just have to live with it... or spend a ridiculous amount of money on 2 new wheels(which isn't going to happen)I do have to mention that I had done 30k miles in it during this time.
1.6 tdci, remapped to 120 bhp, Panther Black Titanium with rear view camera, nav pac and front sensors. Always willing to stop & help in any situation I can. Karma is a beautiful thing.