There's a rubber gasket in the cap that seals it to the valve cover, refer
to part #6 in this diagram http://tinyurl.com/ykd2fh . On older cars, these
often become hard and brittle and fail to seal. If you haven't had a valve
adjustment in a while, usually every 30 K miles, then it might be a good
time to get that done and replace all of the gaskets, #'s 3, 4, & 9. In the
case that your valve adjustment was recent, then it could be leaking because
sometimes mechanics will try to reuse the old parts even though their not in
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