Apply ZEP Heavy-Duty Citrus Degreaser full strength (with a manual pump garden sprayer) to your engine.
Both are available at your local Home Depot.
Try to avoid electrical connectios
Rinse with a gentle stream of water from the garden hose.

May take a couple of applications, but it will safely remove accumulated oily grunge.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022