That looks like your front cover is leaking. See the oil near where the heater return pipe screw is? That seems to indicate the oil is seeping from front cover (either a leaking cam seal, or the U gasket needs replacement). I'd replace both just to be safe --- pretty easy and quick DIY job.

G'luck!

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-Paul-
'01 E430, Sport 72,000 mi
'98 C280, 126,500 mi