Diamond Cut

Corrosion.

I had all four wheels replaced by BMW (under warranty) in 2019, only for corrosion to appear in 2021 on this wheel.  BMW would not replace it again so I'm paying for a new wheel tomorrow, rather than get it refurbished.  However, I've just noticed that another wheel is showing some of this "mould" so I'll need to get a refurbishment done at some stage – I'm not going to buy another wheel.

Sigh.