Today i changed my spark plugs. and when i took out 3 of the plugs and oil on them. 1 in the far back passenger side and 2 in the front in the middle. My car have been misfiring and now i see why. How is oil getting in? I did a search and a lot of people say valve cover gasket? Are there any other ways? How hard is it to change the valve cover gasket?

The front on a Conti isn't bad... the back... not fun.

So more then likely its just the the valve covers? Or could something else be wrong?