1984 300sd turbo diesel - black oil on injectors

Hi I ordered and received new nozzles today and it was a easy pleasant job replacing them. The old nozzles were in bad shape and very clogged up with black soot/mess. I thoroughly cleaned the injectors with break cleaner and installed the new Nozzles.

One thing i noticed when i removed the injectors was that they had what appeared to be black engine oil on the bottom of them where they screw into the engine block. From this I can only deduce that either the piston rings have blown or the head gasket/head is blow/gone letting oil get into where it is not meant to be. Would this be consistent with the knocking, loss of power, and thick black smoke from the exhaust? Do you think i have gasket/head/ring issues or is this normal (I cant imagine)

Thank you for all your help info.

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