Dan, assuming there is not a hairline crack somewhere, try one more time with a new FelPro gasket. Clean the gasket surfaces on both the water neck and the manifold with a razor blade. Wipe down with lacquer thinner. Use a waterpump and thermostat specific silicone gasket sealer.
Smear it uniformly all over both sides of the FelPro, just thick enough to cover. Give it 10 min to get a little tacky before you bolt the water neck back on the manifold. Just snug the bolts up overnight, then the next day run them up to around 25 ft-lb, so you don't squeeze the sealant out while it is wet. Good luck!
Sam