I'm not kidding. Oil in the tubes? You'll have to watch his video series at https://www.youtube.com/watch?v=bA0NtAXiPy0 to see what he found.
Sorry but it sounds the same to me. The work is not trivial.
I have a 2009 Nissan Altima- 2.5 4 cyl. It started misfiring real bad the other day out of nowhere driving home from work. Got the code checked and it was P0302. Cylinder 2 misfire. Bought some plugs to start and see if that would fix it. When i pulled the coils, there was a lot of oil in the first tube and a few smalldrops in the fourth tube. I cleaned that out and replaced the valve cover gasket. Replaced the plugs and it is still misfiring. I took the coils out and put a multimeter to all of them to see if any of them were dead. They all had some juice in them. I am stuck as to where to look now. I fear I may have a warped cylinder or something. Any ideas as to what I should do next or what could be the problem?