Hi Guys,
I finally got the answer from the person I know in MB Germany.
It seems that the internal part of the bonnet has never been painted in black (dark grey) on the 280 SL.
So that is meaning that my bonnet is one aftersale bonnet which was originally fitted with soundpads and primered in black. When it was changed on my car, they took the decision to only paint it externally and not in the internal side.
As it was black when I bought that car, I decided during my restoration to paint it black (i did not know the SL113 site at that time). So I suppose I'm the only one to have one internal black bonnet in the world....
Hope this will help for fuure restorers.
BVest regards.
Vincent R (France).