I prefer the permalube system. Put any cheap, non-detergent 40 weight oil in after the first dealer service. Under no circumstances use detergent oil (probably only the old-timers know what I'm talking about -- if you don't, find a farmer over 80 with only dead tractors, he will set you straight).
Once it gets good and black, just top off once in a while. That pesky drain plug will silt up pretty soon and stop dripping, ditto for the valve cover gaskets, etc.
The filter is solid, too, so you don't need to change that, either -- next best thing to maintenance free driving!
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!