Thanks for your replies. I did not know they were painted.

I had a Mequiars person see this post. He said it was not clear from the picture what the lower panels are made of. He said that the Meguiars Gold Class Trim Detailer works well on Unpainted plastic no matter whether it is black or not.

I will try wax on the lower panels at next exterior detail.

__________________
1992 300D 2.5 turbo diesel. 319 k miles.
124.128 chassis, 602.962 engine, 722.418 tranny.