Do not tighten the Manifold Nuts too much. Where the Manifold Studs screw into they Cylinder Head there is only about 4 solid threads that hold it into the Cylinder Head.

I have a Fair amount of Blow-by and when I had the Manifold off it was Oily but there was no Oil pooled inside of it.
Also in my case the hole for the EGR was entirly plugged with Carbon.

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84 300D, 82 Volvo 244Gl Diesel