Hi All,
I have an X5 3.0d and a 335d Both suffer from rusty hubs, but the 335d is much worse than the X5. So I eventually got around to sorting out the X5. I used a wire brush, fine (too fine I think) sand paper and some Hammerite Smooth Silver following advice on the E90 Post forum.
This is a picture of the state of the hubs on the 335d (Just over 2 1/2 years old and 28,000 mile)
Picture of the refurbed X5 hubs
And finally a picture of my 3 1/2 year old X5 3.0d just because even though it is bog standard (apart from the amp and Xenons) it still looks stunning when it's clean!
Enjoy