Oberon Bar End Mirror Coming Loose??

If the somewhat loose thread on the large outer grub screw comes loose unless you screw it in ridiculously tight, I think I have found the cure.
Wrap the thread with plumbers PTFE tape!

Works a treat...

 

I would recommend doing it as a precaution. They are notorious for coming loose, resulting in the mirror bouncing down the road - it actually happened to someone doing a review on them! lol
https://www.webbikeworld.com/oberon-bar-end-mirrors/

 

Did you read the web bike world review?
He had loctited them in place and still lost one.
The point about the PTFE tape is that it takes up the slack in the threads and even grips, so that even if the screw loosens it won't drop out - rather like a nyloc nut...

 

The self-amalgamating tape is probably a good idea but gripping the inside of the bar isn't really an issue. The only issue is the looseness of the threads of the large stainless grub-screw inside the threads of the aluminium bar-end that doubles as the mirror mount. Winding ptfe tape around the grub-screw threads allows you to take up as much of the looseness as you want, depending on how much you use.
If you prefer to use Loctite that's fine but I think you'd need the right type and more than just a dab, bearing in mind that the web bike world guy had used blue Loctite and still lost a mirror.

Looking at the above (web bike world) picture, you can see that the stainless screw not only clamps the mirror in position, it also retains it in the bar end. Because the screw is such a loose fit, once it comes loose, it comes really loose and will readily vibrate right out.
The ptfe tape addresses the issue, hopefully the right type and quantity of Loctite would too.

 

Wow, that really is a great save.
Well done you