The Screw with the Phillips Head above the Oil is one of the Screws Holding the Governor Housing to the Fuel Injection Pump.
The Governor Housing Screws can be tightened again. But, I do not know the torque. Someone a long time ago posted diagrams of the IP showing the torques but I was not able to find them in My Notes.

The Plug that the Arrow is pointing to is the Plug that covers the Port that the Timing/Locking Pin, A-B Light or RIV timing setup goes into.

It is sealed with a Crush Washer. If you want to deal with it now you could degrease it and put enough Blue Loctite on the Back theads to go completly around the back threads.

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84 300D, 82 Volvo 244Gl Diesel