I have a P3 titanium Kabuki that arrived with the "adaptor" o-ring already distorted and out of place. That 0-ring is much thinner, and really just designed so that your 510/P3 connector doesn't get screwed together so tightly that it's impossible to remove. Since I had a radius to put it on, I ended up just using the P3 connection since at first I was trying to "make contact" with a P3-510 adaptor to a 510-P3 adaptor, which was madness!! LOL, it works much better that way, is all I can say.
The only other O-rings I know of are the ones for the top and the bottom of the tank. Both of mine have stayed seated but I do lubricate them with E-liquid so that everything untwists easily. Mine are the thicker, silicone rings.
I don't know of a small O-ring for the driptip, but I replaced both my Kabukis (authentics) with a Nautilus drip tip as I prefer it anyway. One came with the special "puff-into-your-mouth" squeezy driptip, and I have used those driptips on other tanks and they can sometimes feel a bit loose. I don't think the Kabukis I got had any "drip tip" condensation, ever, or leaking. Yes, they need to be threaded carefully and not too tight, which is best for not causing leaking issues. If I tighten too hard, I will sometimes see leaking. I'm learning "finger tight" is best for most stuff.
Best of luck, you could try removing it to see if your tank performs any differently, is all I might be able to suggest....
Anna