Spray some brake cleaner or something alike, to clean that pump up. Then start the engine and see where exactly it is leaking from. Diesel is really a thin oil, and like oil, spreads. So you could have small leak that spread.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member