I had a call from my dealer to say BMW are putting together a repair kit for these rusty seat bases. Apparently it's going to take them until the end of February to put this kit together but once it arrives at the dealer I'll get a call to take my car in and they'll fix them.
A bit of a wait but at least they're going to do something about it...
320d M Sport Tanzanite Blue with Cashmere Beige Merino Leather interior
335d XDrive M Sport Moonstone with Black Merino Leather interior - on order!