OK, in case anyone want to know what they are, I finally figured it out. They are in Group 68 and are called "Cover for immersion paint holes". There are two of them, part number 113 683 01 10. There is the associated seal washer part number 113 997 0041. Found this through my recently purchased MB 230 SL Spare Parts List (I think it's the dealer edition - 10 097 -- wonderful book).