Possible oil leak from intake manifold?

[DieselScout]

I cleaned my engine a couple of days ago to find the source of an oil leak.

The oil looks like it's coming from inside the intake manifold and leaking from the connection to the air box and pooling onto the manifold.

I've always had oil pooling on the intake manifold on this car and another d24 I've owned.

Anything I should be worried about?
Any way to prevent oil from leaking at the connection?

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[ngoma]

Looks very clean in there, with the exception of the pooled oil. Where is that coming from? Crankcase ventilation? Turbo? EGR?