Interesting, but the part 51120006013 points to item number 4, meaning the rear apron, not the side skirts
It's also not really expensive and that is extra strange, perhaps I should order to find out 
Here it's called the Aero Kit, you can find some pictures online:I see this part is available in Schmiedmann and I was thinking what it is? As it looks it is part of the rare aerodynamics package that came out for the facelift models. But I cannot find any real image of what his apron looks like besides this image
View attachment 290957
Thanks a lot that's the info I was looking for