Could be a number of things, or a combination.

First, check levels, then clean the area.

Pay close attention to the oil cooler lines, the oil cooler, the power sterring hoses, even the A/C hoses.

Once you have everything cleaned, dust some white powder (like foot powder, not the expensive kind of powder) around the area and that will wick up the oil at the leak, making it obvious.

Consider, also, that any oil leak will be above and ahead of the point you see it collect.

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles