The upper part of your Fuel Injecetion Pump (the high preessure part that creates the pressure for the Fuel Injectors) is lubricated by the Diesel Fuel itself. The lower part of the fuel injection pump is lubricated by motor oil that you have to put into the pump yourself.
Many people do not know that the older Fuel Injection Pumps are not lubricated by pressurized oil from the engine itself.
While it is normal after long periods of operation for small amounts of Diesel Fuel to seep down into the Fuel Injection Pump oil sump it is also possible that the Elements (plungers and barrels of the pump; the parts that create the high pressure for injection) ar worn and seeping more than normal.
I would find the drain plug on the Pump oil sump and drain all of the liquid out. Put the sump plug back in and replace it with 40W or 30w motor oil.
Just use the engine as normal but check that dip stick and see if the oil level keeps rising over time due to the Diesel Fuel dilution.
If the fuel dilution seems like it is a lot you have 2 choices if your engine is running good. You can just use it they way it is and keep changing the oil as needed when you feel it is getting too diluted or you can have the Fuel Injection Pump rebuilt which will coast around $800-$1,2000 each.
Also as the other member suggested it would not hurt to run a hose to a container to catch the overflow and keep the liquid out of your boat.

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84 300D, 82 Volvo 244Gl Diesel