Could be a freeze plug -- that will be higher on the block but not at the manifold.

If you have coolant leaking at the bottom edge of the exhaust manifold, it's the head gasket and it's replacement time.

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!