Thank you for your answers. I don't think it was a petrol van converted to diesel, as it's a pain in the ass to do so here in France, thanks to our love for bureaucracy. It seems to be an original 50 000 km, one-owner diesel van. But it was stored for a long time, enough to transform the heat-fan box in a mouse nest. I believe that old muddy diesel was pumped into the fuel injection pump. The CAV diesel filter is clean, hoses seems to be clean also. I have to check the fuel tank, which is leaking, by the way, from its filling port, when the level is too high.
Another picture :