Yes, use WD-40. If you keep using ether, it might blow up the engine. I run wvo ( 1 tank ) and the glow plugs only lasted 4 months. Just put a new set in Tuesday, now it starts right up!

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1984 MB 300SD Turbo

Great googly moogly.

Would you mind posting a picture of those glowplugs, just as a reference point?

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'95 E300D ("Tank") - 231,000 miles
'79 240D ("Biscuit") - 197,250 miles (Sold)
'83 240D ("Ding-Ding") - 217,000 miles (Death by deer)
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"Back off, man. I’m a scientist” ~ Peter Venkman

Probably all covered with nasty grease residue, just like the rest of the pre-chamber and engine.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Check the injector tips. Cold WVO (and WVO is cold on initial start up) will often over time coke/clog the injector tips and effect spray pattern. The fine misting action of the injectors starts to be more of a drip then a mist. This often leads to cold start issues.

He means that it sounds like it has compression. As opposed to an engine with a non-rotating camshaft, that does not sound like it is pumping, because it isn't.

But your engine requires a whole lot more compression than a gasser. You cannot hear that the pressure is insufficient for ignition unless you have none at all.

Note that there exist gasoline engines with pressure relief valves on the cylinder heads, to aid in starting. I haven't used one of those in about 40 years. It was an old Deere with no starter motor. You turned the flywheel by hand to start it. And if you like your fingers, be careful where you put them.