The factory used a bead of silicone like glue/caulk along the bottom edge of the meter and faceplate. As you've most probably found out by now, the meter "clamps" are finicky and not very well designed. Just be careful not to over tighten the clamp screws, the meter bezels appear to be made of pot metal and become brittle with age.
Some of the builders ditch the clamps all together and silicone or hot glue the meters to the face plate.
On my 400 I carefully retained the clamps and put a nice fillet of hot glue in the same spot the factory put the silicone like glue/caulking.
Also, used a black sharpie to touch up the bezels.