Free Stillen Exhaust...?

[AgStacker]

Got my Z a couple weeks ago (09 sport PW 6mt). Bought it used w/ 5k on the odometer. When I was first checking out the car I noticed the exhaust was especially bad *** looking, but just assumed it was stock. Granted it has the Stillen logo on the tips, but I just figured it was a collaboration between Nissan and Stillen, kinda like the Brembo brakes on my boss' caddy.

Please check out the photos in my album, I tried to embed them, but... fail
http://www.the370z.com/members/agsta...s-exhaust.html

After browsing this forum for a week or so I'm now fairly positive this is not the stock exhaust system. Please correct me if I'm wrong...

Sweet right? How much does this system go for installed?

I am a little concerned about the warranty though I gotta suspect Nissan isn't to happy about people moding these cars.

I read this exhaust adds 18 hp? is that true?

Should I have a mechanic check this system out to make sure its done properly, or to see if the car needs any additional adjustments to it's tuning??

Any help is greatly appreciated