Not sure about the oil pump arrangement on the 601. On the 190E gas models, like the 2.3-16, the oil pump is built into the front cover and has a pressure regulating relief valve. If the engine ate the guide rails and pins and stuff in the chain box, and the oil pump/filter/distribution system is similar, it is possible some of this crap is under the seat of the valve and is just dumping your oil back to the sump. On the 2.3-16 engines the relief valve is a steel plunger that rides in an aluminum bore and it is easy for the plunger to gall the bore and then hang up, which gives you zero oil pressure.

How long are you giving the unit to run to "prime" the system? It can take a few seconds to get the pump to deliver enough oil to the filter to build pressure. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)