Hi Gianni,

you need to put the OPEL_KADETT_SPLITTER_STYLE2.GMT in your car folder. Then open the GMT file and edit the material for the paint (wc_team_body1_pa). It is very easy with the 3DSimED.
Then rename the opel_kadett_mask.dds for your car number (e.g. when the number of your car is 35 rename the mask to opel_kadett_m35k.dds) and choose the new Mask in 3DSimEd for the material wc_team_body1_pa as specular map.

If you make the new opel_kadett_m35k.dds very dark in some areas then the skin will be matt.

But as i see from your pictures... Normally the blue of the wheelhouse enlargement should be the same as the blue of the splitter, right? Because the splitter is darker it seems to me that the mask already works because normally the color seems to be darker when it is not so shiny.