That would be your centerpin's insulator. It's the way the Sapor is made. I've tried pulling out the center post T block but failed. It's in there strangely & moves up and down with the centerpin itself. Take out your build, turn the Sapor upside down and push the posts down against a hard surface. If your centerpost is raised above the deck posts, it should push back down. Then try to screw in the centerpin all the way. Test it after by filling it with juice or water or whatever to see if the leak still happens. If it does, wrap some Teflon tape around the 510 screw while you're screwing it in. I've tried to get the 510 insulator out, but wasn't able to get that or any part of the post assembly out (except for the centerpin screw).
Edit: it's a cheaply made atty. my advice would be to try and get a refund if possible. If not try a different top air atty like the Aeolus v2/v2 lite, or the Vector. I posted a link where you can get a vector for $19.99 a few posts up, and it's MUCH better than the Sapor.
alright thanks for the help i'll give that a try, if worst comes to worst, i'll get a different rda