Originally Posted by BUMBLEBEE_SS
whats a roof ditch molding?
Do you see the thin black strip running front to back along the roof just inside the door? That is the transition where the roof panel and body side are welded together. This welding is generally done along a depression or "ditch". Most cars cover this with a molding, although more expensive cars like the CTS use laser welding to achieve a much smaller transition that does not require the molding.
On the RS package the black strip on the roof is body color.
Hope that helps.