I replaced the sheet metal below the trunk. While attaching the license plate lamps I noticed two holes that look like they're supposed to have screws, but the panel didn't have holes predrilled (it had a MB part label out of the box). Anyway, the holes look large for a standard panhead sheet metal screw.
A reply with a description or picture would be most helpful.
P.S. I managed to get the lamps secured. I had to reverse the socket on the left to coax it into place!