"Diesel oil" is not what you're looking for.
VERIFY THE PCV SYSTEM (from the fresh-air inlet, to the hose plugged into manifold vacuum, and everything in-between including the valve itself) before you do ANYTHING else.
Mop it up as-is, maybe wash it into the oil pan with kerosene or Diesel fuel, and drain it out. DON'T run the engine with the solvent/sludge in the pan.
Or just change oil more frequently--but not "20 miles" frequently. Maybe 2K miles.
Consider a bypass oil filter. I get SKY Frantz filters off of sellers on eBay for <$100. You'll need some fittings, two hoses, and some creativity. Buy the right kit, and most of that is included in the box...although I don't trust rubber hose, and I'm not thrilled with their idea of an oil-pan-puncturing return fitting. I'd build something that returns the clean oil to the valve cover...and then switch the return to the other valve cover after a thousand miles, assuming the first side has been cleaned-up appropriately.
With a bypass filter in place and functional, oil change intervals can be GREATLY extended assuming no other problems--no coolant leaking into the oiling system, for example. Keep the oil level topped off, and change the full-flow filter at reasonable intervals.