I'm getting a horrible clicking sound from around my STEERING WHEEL. It's weird because it started after I emptied the ashtray & cleared out all the empty beer bottles under the seat, and my radio broke. It used to be only when I took right turns on odd-numbered days, then I found out my turn signal was on.
Sorry, :naughty:

So there was brown goo on the #4 plug boot (outside?)? And how did you figure it was the no.4 cyl that was knocking? Griott's garage catalog has a cool digital thermometer that you can point at things & display their temperatures. This could be used to determine which cylinder is misfiring, as well as be useful for many other things under the hood, or to see which brakes are being overheated or which are non-functioning.

Anyhow-
The Brown goo: Check in your coolant overflow bottle. If it's similarly funked up with the goo, then you've got yon blown headgasket. At least. Blowed h/g's can be internal, external, or a combo of the 2. I've driven cars with blown head gaskets for 1000's of miles. Ok to do, so long as you keep your coolant topped up. Also- coolant doesn't work very good as oil. It, like, "brown goo's" up.

... Or, it could be that one of your tire valve stem caps has fallen off.:naughty: