Mine does also, 190d 602 turbo. I guess some of the oil leaks past the turbo and the rest comes from the blow-by hose.

I applied some gasket silicone on the cross over connections and it doesn't leak anymore.

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1992 Mercedes 190D 2.5 turbo 5sp manual. EGT+boost gauges. Boost controller set to ~14.5 psi. 1 1/4 turns on full load adjustment. LPG injection. Next in the list is water injection.