Neil,
When I did the 400E over with a new roof I also painted the grille to match, gloss. As new inserts are low cost, I went with a new one for ease of prep and age of plastic for less brittleness! I had the body shop paint it as they also threw in some 'flex agent' as you put on a flexible bumper to make it more chip/stone resistant.
If not in a hurry just drop one off and tell them to paint it whenever they do the next black repair, very common and no match problem.
Good luck,
Tobias MB
4 MBs