It's authentic and I got it cheap on Black Friday from MFS for $12.76. Turns out it was what @AmandaD mentioned because after cleaning the threads real good and brushing them down it finally screwed all the way on. I wouldn't exactly call it buttery, though.There may be an issue with the threading on the base or it may not be an authentic Nautilus. See if you can return it for an exchange. If you can't I may have a resource for you where you can buy a separate base, albeit rare, and attach it to your tank. That will save you money from having to buy another tank.
Good to know because Aspire sells them for $10 bucks and then they want $10 more for shipping! At least that was last time I looked.Evape.us has bottoms for both the full size and mini's.