94 Fleetwood Spark Plug issues/Gap Bridging?

Hey there folks long time viewer, first time poster, but got a really odd condition I’ve never encountered.

Have owned 3 B body cars (roadmasters), and bought a D Body last year around Apr. 22’. It has had some electrical gremlins and whatnot, but just got around to fooling with it this year.

Anyway, was pulling the aftermarket opti the previous owner installed, was gonna throw my Mitsubishi optical sensor I had on standby in it, loctite the rotor etc. Figured I’d do plugs and wires since I was already in there, and the number 8 plug had some serious issues when I pulled it. It’s covered in some kind of black and gray deposits, completely bridging the electrode gap and Definitely causing some if not all of the misfire I was chasing.

I threw some photos up here, hoping someone who’s seen this or played around with these cars a good bit would know what’s going on. It smells of gasoline, not heavy but it’s there, and when I poked with a screwdriver, and tried to clean this mystery substance off I discovered it wasn’t soft like oilgunk. It was hard as a rock, almost crystal like and shattered into a million pieces when I finally broke it apart with my small flathead.
Any ideas? Bad valve guide, leaking intake? Almost looks like oil deposits but then again I have never seen oil rock up or crystallize on a plug.

Dont want to pull the heads, but I can need be. Gonna try to compression test to ensure all is well in there, but the odd thing is last year before it started shutting off randomly it ran pretty good.

94 Fleetwood Cadillac, fully stock LT1, and 125,000 miles. Any ideas? Before I Throw it back together I’d like to know if I need to tear it apart further. I appreciate the time to look at this!

EDIT: This mystery substance is not magnetic. I thought it may be a small chunk of valve or cyl head or something, possibly spark welded to the plug, but none of it was magnetic. Just FYI