Sounds like you have a bad gasket around that plug hole. Might as well replace them all. I just helped my buddy replace the valve cover gasket on his 97 GS. When you go to buy the gasket make sure you ask for the 4 smaller gaskets that go around the spark plug holes. They dont sell it all as one package (at least at NAPA) so make sure you get them all. Pick up some RTV and apply it to the gasket before bolting back on as well.

Pretty easy job. Took about an hour.