I recently purchased a 2007 Mazda6. 2.3L I4. 81k miles, and it is in great condition. The car runs fine, no symptoms of anything amiss, accelerates and idles perfectly, gas mileage is exactly as expected (about 28 MPG).
Since it is new to me, I have been doing some general maintenance, one of which was to replace the spark plugs. At that point, I noticed a considerable amount of oil in the 2nd and 3rd cylinder. No misfires or anything, but I took it to the local mechanic to replace the valve cover gasket as well as the spark plug tube seals. Well, 24 hours after the car got out of the shop I took a look inside the wells, and sure enough, there's about a half inch of oil that's accumulated around the plugs. The mechanic said there didn't look to be oil in the piston, where the plug ignites, and like I said the engine runs fine.
So, what else could possible be causing this leak? I'm returning the car to the mechanic on Tuesday to be inspected, but in the meantime I was hoping to get an idea of what to ask and think about.
Thanks for any help.