Manifold gaskets

Alright, so a few months ago before installing my jba longtubes I called up JBA and asked if I was going to need to replace the header gaskets when installing their setup. The guy basically told me that the stock gaskets on the GT are the best than money can buy and that I should have no problem reusing them. This is the first I ever heard of reusing gaskets, but I figured oh well my knowledge on things isn't all that as I've only had the car a year now and haven't done anything myself mechanically (gears sucked tho! ) anyway, my friend who had helped me install the headers told me that I should have bought copper header gaskets instead of the thin junk at the dealership.
Basically my problem is this: I turn the car on in the morning and I can hear a loud exhaust leak (yes I'm sure that's what it is) but it goes away as things warm up. Should I try to replace the gaskets with some of higher quality and see if it fixes my problem? My buddy also told me I may need to get the headers machined if they weren't perfectly flat and that would cause that also and I really hope that's not it. Anybody else with JBA longtubes experience any kind of these fittment problems or have some sound advice for me? Oh, and yes, the headers are tightened down as tightly as possible so no one asks...
If I decide to go with copper header gaskets, anyone know where I can order them? Are there advantages or disadvantages to having these?

Thanks Guys