Could be power steering, both of mine leak a little but I notice it on the glow plug relay not down where you are mentioning.

What about oil cooler lines? They are sometimes hard to see leaking and since the thermostat that controls the flow to the cooler does not open to the cooler unless you are running down the road then the oil does not drip straight down but gets thrown back by the wind.

Check around the metal crimp fittings on the cooler lines to see if there is any sign of oil there.

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique