If an LED has that little plastic ring around it

I forget what it is called, but Convoy for one has it.
When replacing the emitter, how do you mount that ring?
Do you use glue or?

Are you talking about the gaskets that are put around the LEDs?
Those are put in place by simply placing it around the led.
Make sure you have the right gasket for your LED.
Meaning : XML2/XHP50 Leds need 5050, XPL need 3535, …

Also try to see if the top diameter is for reflectors 7mm holes or with 9mm hole (diameter in the base) .

Not the gasket. The small plastic washer. I saw what it is called, but forgot. Some kind of shield.

So, not these?
https://convoy.aliexpress.com/store/group/Gasket-Lanyard/330416_512723652.html?spm=2114.12010608.0.0.64d4739479zmkE

I can’t remember what it is then :zipper_mouth_face:

http://kaidomain.com/Flashlight-DIY-and-Tools/Misc-Parts/S028303-20mm-Transparent-Plastic-Insulation-Gaskets-5pcs

Like these?

I’ve only had one light use this thing, and it just sits on top of the LED MCPCB, it’s held in place once everything is put together.

Edit: I see OP did mean the centering gasket after all.

This:

https://www.aliexpress.com/item/32575732360.html?spm=2114.12010612.8148356.12.2ed02336DOVvfU

How is it secured? When I took apart the L6, I had to use some force to remove from the board.

As you can see, it is called a ‘gasket’ and is used to align the LED in the reflector hole.
Usually they are not stuck on with anything, they are held in by the reflector.
Heat could have melted the plastic and made it stick a bit.