That's an oil separator on the inside of the cam cover.

If the turbo has been replaced, it points to an internal engine problem. Unless he replaced the turbo with a "new used" unit that was also bad....

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