AVguy:
You have a point about the timing belt. I checked the manual and sure enough, they say check it out at 30k miles. Touché. However, I would never, never have asked the dealer to check the timing belt unless there was an issue. I would submit that GM might make an effort to highlight that issue in products with the interference engines (that is, engines that damage valves when the timing belt breaks during operation).
Okay, you have a point again about the valve cover remark. What I did was take off the plastic “engine cover” first and then the plastic “valve cover” in order to access the valve cover gasket—the valve cover gasket was leaking oil into the spark ports which is the subject of this thread and is likely failing on everyone’s car.
Regarding the timing marks, the timing marks on the cam gears would not stay aligned on my car because the intake cam rotates out-of-position after aligning the gear marks. Presumably, this is due to valve spring tension, so it is difficult to maintain position, as I pointed out, without that little gizmo that locks the gears in place. I thought that might be related to cylinder compression, so I removed the plugs.
In any case, the car is repaired and works correctly.
Cheers.