There is also water pump lubricant (soluble oil) in some, if not all, coolants. You will see small (1-2mm) diameter droplets of colorless oil floating in the radiator neck or coolant tank, or a sheen on the coolant. You may notice them more when you drain the coolant into a larger vessel where they can float free rather than sticking to the sides of things.
Watch the coolant tank -- if you start getting a ring of blackish oil around the edge of the coolant, you probably have a problem. Isolated oil droplets aren't a problem.
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!