My 4 year old X5's are starting to rust. They also have a crummy system for seating the dust cap screws - they're easy to strip. I lost one and by the time I noticed it was missing, it had done some damage to the bearings. I ended up replacing it with a screw with a coarser thread.

I'll be replacing them with X1's this year. (It would be nice to find them on sale, but so far no dice).