another thought i had the other day, was if you have any steel 55 gallon drums, put a strong magnet on the bottom of the barrel and it will magnetize the whole barrel over time. After a few days it will start to pull out any ferrous material in the oil. If you have a weaker magnet, then it could be circulated around the barrel somehow so more oil will come in contact with the steel container or magnet. Maybe mechanically filter it first to remove the bigger stuff. For the record, I'm still not recommending using motor oil in your mercedes diesel. At my work, we're going to start toying with distilling diesel hydrocarbons from use lube oils. I've heard figures of people getting anywhere from 4 to 7 gallons of usable diesel from oils and the left over they use to fuel their distilling furnace. I'd imagine that the diesel you distill off might not have enough sulfur in it (just like at the pumps now!) so It might need some Biodiesel mixed in or the powerservice additive.

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'82 240D 224K miles manual transmission
mods: wooden 4by4 bumper, EGR delete and older EX manifold without EGR port, glass pack muffler (cheapest replacement muffler), rebuilt bosch injectors with Monark nozzles

working on: aux electric fuel pump, coolant/fuel heat exchanger/filter head, afterglow, low oil pressure buzzer/LED