Whilst washing the car this afternoon I noticed that one of my rear alloys has what looks like some slight bubbling right next to where the tyre valve is. I gather this is common, is there anything I can do to stop this spreading or is this something that occurs through time and will need repaired by an alloy specialist? When cleaning the alloys in particular I try not to use too many products on them as I would image some products are better than other and just normally use car shampoo and water. Thanks.