A wonderful gift from New Zealand today!

Good looking pipes. I did not use silicone. The service manual makes no reference to using silicon. The factory sure had a lot on. Took forever cleaning that #rap off. Followed the manual and got very lucky no leaks.
 
An interesting point this leaking carry on.
I don't know if the Factory use's any sealant at the port here, I've not ever removed a header that's never been removed before.
So apart from applying sealant at the port here, my set up is Identical in size/area to the factory Header, so with the stock copper seals fitted I don't see why it would be any different to stock.
Possibly it is the way the new header is fitted ?
I don't know that, so really can't comment.
 
Now that she is getting a custom tune, any guesses on how much power I will pick up?

Viking header and midpipe are what I installed.
 
just a little note my 08 had a slight leak even with new copper gasket properly torqued, easy fix Selleys 401 silicon is heat resistant and is Clear so no ugly copper or black colour of other sealants works a treat, in fact I ended up putting it on all exhaust joints afterwards on the several exhaust system changes that I made and never had a leak
 
Your header was a better fit then what I took off (stock). Saw no need for silicon. Did take my time with the torque wrench. Slowly tighten all three pipes evenly and did top bolts first then the bottom bolts. then went back and did a final torque check on top bolts. No silicon and no leaks.