I agree with the Guru.

The key is to a successful reseal is to really clean the corners where the cover meets the head gasket. That is a point that is prone to leaking. There is a crevice that you need to use a pick to clean out until you see the metal edge of the head gasket. Old sealant in the crevice will cause problems. Also use a non-oily solvent, like alcohol, to clean the surfaces before sealing.