onekutcha

Hello all,

I have a 1999 Audi A8 4.2 Quattro.
One day after I started the engine the Engine Light came on.
I checked the ECU Memory and it said that one cylinder misfired. I did not give it a big deal since it happened basically once and since the engine was running smooth.

After a while a started to hear some very faint vibration type clanking noise when engine was idling from the passenger side around the front corner of the valve cam area like this noise was coming from the camshaft compartment from around the first cylinder section (that is the closest to the front of the vehicle on the passenger side). Sorry, but I am not sure what is the cylinder number of that specific cylinder, but you get the idea exactly which one I am talking about.
The noise did not become louder with the RPM, but I could hear that by increasing the engine RPM the cycle frequency of this clanking noise was also increasing so it was related to the engine RPM in some way or another. After an RPM of around 3000-4000 RPM it was not hearable possibly because of the normal engine sound.

So I decided to look under the Valve Cover to see what is going on in there and after following the Valve Cover Gasket Replacement Procedure from www.audipages.com/Tech_Articles/enginemechanical.html I take out the Ignition Coil of that specific cylinder and I see that the Spark Plug Connector is soaked in engine oil (which should be totally dry and clean!!!), moreover the area of the Spark Plug Connector that goes on and covers the top of the Spark Plug, that rubber is broken.
After opening up the Valve Cam Cover I see that the Valve Cover Gasket that goes around the Spark Plug tubes to keep the engine oil out of the Spark Plug tubes, is totally missing!!! -Where did it go???
The 3 other Spark Plug tubes have it all but this one was missing. That Spark Plug tube is full of engine oil covering the top of the Spark Plug and while I was cleaning out the dirty oil meticulously from that Spark Plug tube I have find some oily melted (?) rubber particles that I think was what left of that tube gasket.
I am not sure.
My next step was to take out the Spark Plug and I have cleaned that as well.

Here are my questions:
How could the Spark Plug tube Valve Cover Gasket disappear?
Was it simply burnt somehow? (The Spark Plug itself felt tightly screwed onto the Cylinder Head! So, I don't think that any combustion could come through into the Spark Plug tube.) (?)

Or was it some kind of electric issue (little occasional short circuits because of the broken Spark Plug Connector that in time made the rubber gasket porous and later dissolved in the engine oil?
Why was the Spark Plug Connector broken at the Spark Plug connection side?
I am going to replace the Valve Cover Gasket and also the broken Spark Plug Connector with new ones that should arrive tomorrow since I've already ordered them, but I am not sure if it will solve the weird clanking noise problem or will it?

Please help!