First check the pressure with a manual gauge. M110's use an electronic sending unit for oil and coolant gauges.



Second (or first actually), check the lower oil pan. All too commonly on the W123's, the pans have been smashed by impacting a parking block, curb, etc. which forces the sheet metal into the oil pickup tube impeding the lubricant flow.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now