How long did the engine sit between running fine and not starting?

My first suspicion is that you have air in the fuel system. Crack injector lines and crank the engine in 20 second increments, waiting a minute or three in between, until you get a good strong pulse out of an injector. Tighten that injector nut and continue until you have the same result or (what I've seen more commonly) you get through about half of them and the engine starts. Then tighten the rest.

The glow plug covered in oil is a bit disconcerting, but we can come back to that after the above.

Second idea: Have you verified that the glow plugs are getting 12V when "glowing"?

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.