unless you didn't bolt it down properly in three stages to reach the proper torque , say it's supposed to be 60 lbs , you tighten all the bolts in the right order to 20 lbs ,then all at 40 lbs , then all at 60 lbs.there is a specific order in wich this has to be done or it will leak.If you followed the procedure properly and it still leaks you may have a warped head. simply hold a carpenters steel framing square (or something you know to be perfectly straight) on edge in all directions and look to see if it's flat and has no warpage.
if it is warped a machine shop will plane it down for you.this will take away combustion chamber volume leading to a slightly higher compression equaling more POWER arrrrgh.
since the head is at the machine shop, you may as well have it ported and polished,maybe gasket matched and unshroud the valves , an extra hundred or so may give you another 30 or more h.p.without changing the cam or the chip..mike