Replace the heater pipe 0-ring, and if the belt tensioner didn't return to the start mark when you loosened it, or the rubber shows signs of deterioration, I'd replace it -- the final clue is that you won't be able to correctly tension the belt. Idler roller comes with.

New valve cover gasket, and while you have access to the chain, check for stretch (usually minimal on this car).

New cap and rotor if the old ones are bad, and expect to replace the rotor carrier and shield, they usually break coming off.

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!