Chuck
Just my two cents, but I'd probably first try keeping the o-ring, but using RTV in the metal-to-metal contact area, keeping it off the o-ring and out of the ring groove. Also, I'm sure you already thought of this, but make certain the o-ring is not twisted or pinched when you install it in the groove. Double-check that the o-ring is not cut or torn anywhere, too. Oh, and you can easily overtighten the bolts in most o-ring applications, causing the o-ring to squish out of the ring groove.
O-ring seals are ususally pretty foolproof. None the less, it is a pain to chase down these little gremlins. Good luck.
Eric