Toyota Repair: oil in sparkplug, valve cover gasket, toyota camry

Question
for a '89' toyota camry w\190k miles: when attempting to change sparkplugs i encountered oil in the #1 sparkplug.whats the problem and how can i fix it?

Answer
The problem is a leaking spark plug tube, the valve cover should be removed, the tubes are threaded on both ends, they can be removed with channelock pliers or a special pipe removal tool, after the tubes are removed the threads are cleaned and new silicon sealer applied to the threads where they go into the cylinder head, the valve cover gasket is replaced at the same time.