Centerline and Mark both made good points.
Are you 100% sure the leak is not coming from the head bolts? What type of sealer did you use? Try running the engine for e few minutes (enough to get warm but, not hot). Pull off a valve cover on the side that's leaking and see if you spot any drops of water running out from under the head bolts. I have had a problem in the past with ARP thread sealer.