I went to an exhaust shop to put in an aftermarket header, but it leaked so they had to put the stock one back on. I popped the hood when I got back home to make sure everything was okay and I saw some smoke coming from the header. When I called them they said it it probably the wd40. The car seemed like it ran fine. I also had a hi flow cat installed so I can't tell if it's louder cause of that or cause it's leaking. Am I just being paranoid?

 

I don't know why they'd use WD40 to install an exhaust manifold, but if it was WD40 it would all burn off within minutes. If the manifold is smoking where it meets the head for more than a few minutes, it's leaking.

 

They used it to take off the stock one.