When I worked for MB in the mid '70s, all cars -- and engines -- shipped from overseas were covered in a protective coating of cosmoline, which was routinely removed with a mild solvent during dealer prep. I think that's what's baked onto my engine.

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'91 300D 2.5 Turbo 330K
'00 VW TDI Golf, 190K
'67 BMW R50/2
'73 Norton Commando Interstate