I had the headlight doors chromed as one piece on my W111. It is a similar type of assembly with rivets. Around the rivets, the chrome is somewhat flawed. I believe this to be from trapped solvents or acids used during the process. I was warned about that in the beginning, so no surprise. It hasn't gotten worse in five years, so maybe it won't change. Who knows. That is why they won't guarantee it.
The best of course is to remove the rivets and chrome as multiple pieces. I too am close to refinishing my intake cowl and will look into using a stainless rivet that is highly polished.