The same thing happened to me on my W221 S320 ,picked up my first stone chip,it was not big,my insurance says use Autoglass,so their guy came along he looked at the chip and then went into the spiel about it might not repair,well this was a small chip nowhere near the size and depth of yours,he started to pick at it after a few mins he started to repair it saying he would try his best,but he seemed to do things a bit half hearted,when he had finished it just about looked ok but after he had gone I went out for a drive and noticed where the repair had been there was now a dull white patch so I got onto Autoglass and said I was not satisfied and they sent somebody else and we agreed to have a new screen fitted,if you go that route make sure it is the right one as depending on the extras fitted to your car, getting it out was crazy they have this weird contraption of wheels and yellow cord and this is fitted to the inside of the screen and it is wound by a handle well it did not work and he used wire in a sawing motion to cut the adhesive was I glad when that screen came out,it left me wondering if Autoglass have decided that they have to fit more screens,just a thought