Reviving an old thread here but thought it might be worth it.
Had an M5 for about 6 years without a single swirl. One wash at the dealer post service and it was a nightmare. Of course the dealer wouldn't accept it. Swore up and down it was hand washed and properly. Even went so far as to insinuate the swirls had been there of my own doing.
After that, I purchased one of these for all of our cars and always keep it in the glovebox.
Hope it saves you from paint damage in the future.
https://www.carboncollective.com/pro...wash-pvc-hook/