Some of the models have injection pumps that use only copper crush washers to seal the delivery valves. No rubber "O" rings to get eaten up by the WVO. I do not know a list which models but I have read my 84 300D dose not have the "O" rings in the IP.
I believe the one after 86 have the IP "O" rings and some need a special splined socket in order to change them.

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84 300D, 82 Volvo 244Gl Diesel