Same thing happened to my 156 - dealer in Galway washed it after some minor rattle fixing, leaving lots of lovely swirl marks - on a 3 month lod car. Really pi$$ed me off as I'm so careful washing it myself and only with clean sponges etc.
Anyway, I spent a lot of time checking out the various options to fix it - be very careful what you use - most if not all are abrasive in some way. I settled on Autoglym Super Resin Polish in the end - applied it a few days ago (was surprised how easy it was to apply and rub off), and most of the swirl marks are now covered - not all though, so might give it another treatment in a week or so to improve things just that little bit.
One very important note - make sure you buy the Autoglym perfect polishing cloths to apply and remove it - they're the only decent non-scratch cloths you can get in most stores.