I have talked with several engine builders that recommend the red rtv. One even said with 3/8 flanges milled flat, no gasket at all is required. We will use a bit of RTV.
Let me spew some info I have gained on header gaskets. As Greg said, re-torquing after multiple heat cycles is essential. Is is also still required when using locking hardware of any type. The locking hardware only keeps you from loosing the bolt. When using any gasket that can "crush" or get thinned under pressure you will still loose the effective seal at some point and reduce the gaskets chance of not burning by and creating a large leak. When the gasket thins permanently the bolt with locking hardware will stay in, but is no longer torqued the same as when you put it in. The clamp load is lost. This is one of the benefits of the rtv. When you torque the header, most of the rtv is displaced. you will have metal to metal contact in some areas and the rtv only remains to fill the voids. As Greg also said CLEAN, FLAT, UNDAMAGED surfaces are best in all cases. By the way, this thought process applies to most compressible gaskets and yes, you can over torque compressible gaskets. That's another talk. Hope this helps. Good Luck. Spewing finished!
