Can't get these damn headers to stop leaking COOLANT!!

Look at the ARP catalog and get longer bolts. The bolts are short, the flanges are thicker, and there's not enough thread engagement for the sealer to seal solidly. Also, clean the holes with a tap and brake clean before you try more silicone. If there's any residue from antifreeze the RTV/sealants wont stick and it will leak.