Ok... Will try to find a compression testing tool tomorrow. thanks.

I think the confusion came from your titling the thread with "electrode" (which I think is what you mean), and then in the first post, say "injector" instead of electrode.

Yes, if your coil tubes are free of oil, and if you have oil on the electrode side of the plugs (internal to the cylinder, isolated from the oil under the cylinder head cover / valve cover) then that oil is probably coming from elsewhere. There are a few options, including valve stem seals leaking. Having all of them equally wet would be a clue. Is it liquid, caked residue?

M54?

Yes, it is an M54 engine. The oil was in liquid form, but there is also caked stuff on there. The liquid oil has dried out now (please see photos below). But the threads of the spark plugs are also quite dirty with dried out oil and tiny little particles of something solid.

Replace the plugs and monitor. It's my guess that this motor gets short trips and does not come up to full operating temperature, this results in sludge forming in all sorts of places, including the spark plug tips. The oil above the flats for the socket comes from the valve cover gasket, specifically the two pieces that have 3 circles, but the oil below the threads is coming from a source inside of the engine -- rings, valve guides/seals, those sorts of things. Another source would include things like the CCV system. I think you are having trouble with a vehicle that takes lots of very short trips in cold weather, in which case you can't do much beyond driving it more. I would put new plugs in and watch for the misfires to return. Perhaps in a month, pull the plugs again to inspect them.

I had similar issue with my M52 engine (oil on electrode side of spark plugs) on my 1997 E39 standing at 215K miles on the odometer. It turned out to be the valve stem seals, which I replaced. They were hard, brittle and wider than the valve stems. Do you also get a puff of blue smoke when starting the car only after it has sat for a while, e.g. in the mornings? That would be a definite give-away your issue is similar to the one I fixed.

@jdstrickland: You must have a crystal ball or something! Yes, the car is driven only a handful of miles each day. I will follow your suggestion and drive it a bit with the new spark plugs and see how it does. But... please! Could you explain HOW you knew this was the case? :-) Curious to learn :-)

@X5only: I had not paid attention to the exhaust in the mornings but will do so now. I am off to doing some google searches on valve stem seals. I bet that's the source of the problem because I know those have never been replaced (I am its only owner!) :-)

Thank you both!

Valve stem seals is not a typical maintenance item and it's a very involving task, as such it's only done when it sure is the culprit for engine issues.

@X5only: That sounded like a super nice way of saying: "Sorry but so far you don't seem qualified to do that job!" jejeje... Thanks for the gentle tug on the arm! :D

So, with the new plugs installed, the misfire is still there. For now it is only reported for cylinder #5.

I did clear the codes and they were gone for about 2 minutes, though the misfires could still be felt during that "clear" period. But then the misfire code returned and the SES light is back on.

I am going to try swapping the ignition coils again, and see what happens. Good thing I have them labeled... :-)

Classic example of oil fouled plugs. Confirm plug is firing after coil replacement.
If yes, then you need to do a compression test and a leak down test. A bore scope can be a problem solver for your vehicle here by looking into the cylinder for bore scoring, valve sealing and a peek in the intake side will show if oil is leaking into the intake manifold.