Northstar Engines and System Technical Discussion Discussion, Oil Coverd Spark Plugs on Northstar in Cadillac Engine Technical Discussion; I have a 93 Seville STS with a Northstar -- While changing the spark plugs, I found the rear bank ...
Remove the rear cam cover and replace the round, 0-ring type seals around the spark plug wells that seal the cam cover to the spark plug well.
Otherwise, forget about it. It really doesn't cause any problem so unless there is some other reason to remove the cover I would leave it alone.
Oil seeping into the spark plug wells of DOHC engines like this is not that uncommon at high miles and long years. Wipe them out with a rag and forget about it. It will never get very much oil in that area due to the fact that that well is above the level of oil in the cylinder head. All that is seeping in is casual oil splashing around and is not a pressurized oil leak.
Unless the oil becomes very deep in the spark plug well it will not likely cause a problem. It is quite common to put grease inside the spark plug boots to seal them to the plug to keep moisture out and to keep them from sticking to the spark plugs. If grease on the inside then oil on the outside of the boots is not likely to cause a problem.