[d4springer]

I'm not sure if it's a definite solution but I use Meguiars Hot Rims to clean my wheels (it's non acidic), I have also coated the alloys with Gtechniq C5, basically spray on the Hot Rims and clean off with wheel woolies or hand mitt.

On my previous 330D (with the M Sport Brakes) I used to wash each wheel individually then I would dry off the discs with kitchen roll as quickly as possible. For me the rust build up seemed quicker in the winter? I started using the Hot Rims and I noticed that if I sprayed the stuff over the whole wheel, discs and hubs included, then cleaned everything with a hand mitt, ie cleaned all around the alloy, hubs, discs and calipers, rinse off and no rust was forming!

I've carried this routine on with the M3 and so far again no rust is appearing after cleaning the wheels. I'm not sure if there's something in the Hot Rims which is preventing the rust build up but it just seems to be working for me anyway.