Dead coolant or use of green stuff instead of MB coolant can cause serious corrosion on aluminum heads -- my sister's 92 Volvo 740 did this, probably caused the head gasket to blow on the highway (or the radiator nipple blew off, hard to tell after it quit running!). Huge pits at the blind water passages, ate almost all the way into the cylinders. Head was junk (warped horribly), so I replaced it.

If you have changed the coolant every couple years, you won't have any corrosion.

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!