Yes try running on a bottle of fuel. Your whole problem could have been something other than good fuel pumped into the tank. Try to fuel only at higher volume places.

One problem is smaller diesel volume places are supplied by bulk carriers. Between loads of different products sometimes they are not cleaned out well. You can get whatever it was that was not cleaned out. I have even found close to bunker oil in cars. Or what it seemed like. Places that sell a lot of diesel will not take supply from other than dedicated tank carriers. That's why in general large truck stops are the best places to fuel.

It also could be a lot of algie and water. I never see it as far north as we live. So identification by me is impossible. Getting water pumped into a car is far from scarce. You can never be absolutely positive but there is no reasonable way engine oil or whatever it is. Got into that filter other than from the fuel tank. Do not run the engine on it.

You will want to change out or remove and flush out the secondary fuel filter as well. That black stuff will be in it. Even before running on a bottle . Remember the bright side as well . You do not have a cracked head or blown head gasket.