Sounds like your cam seal is gone. The cog is on there with a lot of torque, so you are going to have to jam the cog before you can loosen it. I used a 3 foot cheater pipe to get mine off. When you put the new seal on, make sure to clean the surfaces well with brake parts cleaner and glue the seal in place with silicone. They like to pop out due to excess pressure from bad PCV valves and the silicone prevents that. Also, the fully seated position is about 1/8 in below the surface, not flush. While you are in there, you might as well get a second cam seal and do the front crank seal as well. They are the same seal but the front main comes with the oil pump gaskets that you won't use and will just cost extra money. Expect to spend around $13 for both seals with tax. If you do the crank seal, expect it to be VERY hard to get off. Refer to this thread for the how to on replacing it:
http://geometroforum.com/topic/3083546/1/
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(Note: the car sees 100% city driving and is EPA rated at 37 mpg city)