'04 R53 MCS Had mushrooming, but fixed it. I put camber plates and strut tower brace. Had 17"RFs, went to 18" NonRFs and am now on 17" Non RFs. Fixed it a few years ago and no mushrooming since.
Wife's car '06 R52 MCSc Had mushrooming, but fixed it. Put on strut tower brace. Had 17"RFs, went to 18" NonRFs. No mushrooming since.
The reason your mushrooming has returned is because you are using a JCW brace. That does not do anything for mushrooming, IMO, mostly for looks.