Fleshlight/fleshjack Users: Maintenance/assembly Question

[JasonPharae]

In my fleshjack (turbo ice) there's a hard plastic ring which is supposed to fit somewhere near the open ("orifice") part. I never noticed it before because it was firmly attached, but it recently came loose and I can't figure out how to put it securely back in place. If I try to just press it into the opening, it isn't snug and it sort of "rattles" when I'm thrusting; often it totally pops out and takes the sleeve with it.

Anyone understand what this plastic ring is? Is there a way to get it to sit in place firmly, besides just pressing it down? Could I glue it?

Cheers, gents!