I was talking to my local BMW dealer body shop about wheels. My plan was to put Alpina wheels on and keep the standard 16 inches for spare. One of them is a bit damaged, nothing serious, so I asked about re-coating it. his reply may be relevant here. BMW do not recommend refurbishing and re-coating alloys because of some wheel failures. One incident in germany of a wheel failure on an 850CSi at 250kph killed everyone in the car. So BMW refused and recommended against repairing the wheels.
Something, I am assured, to do with atmospheric chemicals in the exposed magnesium alloy being tapped by the new coating and corroding it from inside, whereas in an unrecoated damaged wheel that doesn't happen.
that may all be a load of salesman's bull to get me to buy the Alpinas, but I had already led him to believe I was buying them anyway, so he had nothing to gain.
For what it may be worth.
Peter