Varia UT800 Mount is loose

I have a UT800. Over the last month or so, its started wobbling and shaking during rides. It has not fallen off, but it looks like it might at any point. The problem is not the out front mount. I have replaced the entire out front mount with one I had spare and which has never been used before. Today was the first time I mounted it on the bike and loaded the UT800 onto it and the light still wobbles. The ring around the mount that fastens to the UT800 case is loose, not the out front mount. I have removed the mount from the lamp as attached it to the out front mount and it is still loose, so its the attached bit that is worn. I am looking for a replacement part, I would like to know the correct Garmin part number so that I order the right thing. 

Please see attached pictures

Many Thanks

John