No, usually those o-rings just cause the lifters to rattle, not the main bearing oil pressure to drop.

The oil pump won't get straved by a loss of pressure, it draws right off the sump. I'd be more worried about the main bearings being damaged from oil starvation. A new oil pump will only fix the problem if the pump is bad -- note that at least one other poster HAS had a 603 oil pump fail.

Did you change the filter to a known correct one? I don't know what the filter housing is like on the 603, but on the 617 incorrect installation can dislodge a seal on the filter and cause low oil pressure.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!