Yesterday I replaced the valve cover gaskets on the 540. Well, I found the plugs were completely submerged in oil (I wish I took pictures; you couldn't see the tops of the plugs) I have no idea how the engine idled smoothly let alone even ran.
I attempted to get the oil out of the coil area as best as possible, then drained the rest into the cylinders. After starting the engine heavy blue smoke was coming from the exhaust (from the drained oil). The problem is my gas mileage dropped a lot, about 6-7 mpg after the valve cover job. So my question is did that oil kill my O2 sensors, because I can't think of any other reason for the sudden mileage drop.