Check your fuel lines for leaks, too -- if you don't get clouds of white smoke while you are cranking, you don't have fuel going in, and it won't start til you do.

The suction lines to the hand pump are the usual problem -- they get old and crack, and air gets sucked in, so that the IP has air in it. Takes a while to pressurize the injection lines properly if it sits for a while. This can also happen to a badly worn IP -- the fuel leaks out of the plungers overnight. You'd have fuel in the oil in that case, though. Hand pump can leak, too. If you don't have the new "thumb" pump, get one and install it next warm day.

I'd change the oil to a full synthetic, probably 10W-30 for the winter. 15W50 is too thick for your car if it won't start right away.

I'd also check the chain stretch and IP timing -- late timing will make it start hard cold.

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!