I have an oil leak and there is oil on top of my valve cover and a little oil leaks down in my spark plug holes. I replaced the seal around the valve cover and i replace the oil cap and it still leaks. I have a pretty good leak. I think it may be the rear main seal or front main seal. But i really dont know alot about that. When the oil leaks on the ground its is around the center of the car. Please let me know what i can do about this and what it is. Thanks.