just installed an aps twin turbo kit on a buddy's 06 GTO the head to flange reused the stock stamped steel gasket, the outlets of the turbos used copper RTV, of course the car is getting buttoned up this week and tuned so I can't give you any results, but thats what the kit called for and i haven't heard of any issues with it. Just make sure the flanges are perfectly straight and a good thickness to prevent warping/deflection etc. I know the flanges on this kit are a solid 3/8ths of an inch. Also choose your fasteners wisely thats a VERY high temp area and certain fasteners like to fuse themselves in place.