New studs and nuts might be in order too. Sometimes there is just too much wear between the threads and/or the lock washer is toast. Those and a new gasket are usually the best way to fix it for good. You do have to go back and re-torque them after a good hot/cold cycle.

Honda has some nifty nuts for their manifolds that have a wave style lock-washer that is supposed to be superior to the split style.

Good Luck,
Michael