Dumb ass maintenance problem- sorted?

Need a leprechaun, poke him down in there he won’t come out without it. A 6” tall woman would probly work just as well.
 
my guess would be the plastic ring that stays on the quart oil bottle when you pull the cap off?
Oh heck if its that it float past the neck someday. If its that I wouldn't sweat it. It won't leave the tank. I'd worry a little if it was that seal paper. But it will probably float also.