How to fix tooling split "cannot knit surfaces" error?

Hi,

So I am trying to make a seat mold for a carbon fiber seat, and I've made my parting line and parting surfaces. I've also created knitted surfaces from the top and bottom surfaces of my seat for the core and cavity. But when I run tooling split, I get the error, "cannot knit surfaces". I know this has something to do with my surfaces having gaps, but I'm not sure how to find and fix them.

I can't attach the file since it says it's too large, but here's the link: Dropbox - 2016 seat_Mold.SLDPRT

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