No, this exhaust is off a real NISMO. I preferred this one to the S-Type because it had an X-pipe instead of the S-tune's Y-pipe. This exhaust is one of the main reasons a NISMO made more HP, than a regular 370Z. I believe it helped make half of the addition 15-16 HP that a NISMO Z had over the regular Z.
As far as a new seal (gasket) kit goes, I dunno, maybe $30-$50? I haven't looked into it because the seal on mine was fine.