Benjamin O-ring for DonnyFL adapter?

I purchased a 1/2-20 DonnyFL adapter for my Benjamin Marauder rifle. The adapter does not have an o-ring on it, but the end cap of the Marauder does. Do I need to transfer that o-ring to the adapter? If I do, the adapter does not tighten flush to the barrel shroud - the o-ring doesn’t go all the way in like it does on the original end cap. Not sure what I’m supposed to do…
Thanks!
Mike
 
Oring isn't needed
Thank you!
No o-ring needed for his adapter.
The Marauder was first introduced with the ring and has never changed. Kinda like over engineering but through the years it was more cost effective just to leave it alone then re designing another cap just to remove it.

No o-ring needed for his adapter.
The Marauder was first introduced with the ring and has never changed. Kinda like over engineering but through the years it was more cost effective just to leave it alone then re designing another cap just to remove it.
Great, thank you!