What is the best way to replace the oilpan gasket on a 1984 300ZX?
There is not really any easy to do it. You just have to sit the new gasket around the rim of the oilpan and bolt it back on. Just make sure that the gasket is centered or it will not make a good enough seal. However you could use a small amount of sealent glue or something simalar and stick the gasket into place before putting the pan back on, but only a very small amount or you will create a gap.