Is it necessary to replace the gasket between the head/header when installing a new header?

 

not on a fairly new car that hasn't had the header changed before.

 

Ive reused them before with no problems. But its always a good idea to get a new gasket if you can but its not necessary in this case.

 

It's cheap...so why not; I think there are some that would classify this as a "wear" item. J/K You would be fine with the old one as long as there is no visual damage. Personally I would have one just in case, before I start with the work. Just to be safe.