I am using anti-sieze on my glowplugs. Not sure of the formulation, but I can check. So far I've only replaced glow plugs on the 1987 300D with aluminium head. I'd use the same compound on the iron head 1982 300D as well.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles