I think we should go beyond removing the head and replacing the gasket. There is no inherent technical reason for the copper gasket to "leak". As Martin said, if the head has been on for a relatively short time frame removal should be simple/easy. But, determining where the leak was, and why, is important. How was it decided the gasket is leaking? Was there an external leak or combustion leak or what?? If the mating surfaces are flat and without damage and if a reasonable multi-step torque procedure(without over torque) has been followed the copper gasket will withstand cylinder pressures more than double that which a stock engine can produce. It should be noted the introduction of detonation can not only destroy gaskets but also mechanical parts. Using a pliable sealer at the threads of the 8BA style engine is helpful in stopping coolant leaks around the bolts. Of course, a careful look for any cracks is also advised.