Replace before you have to pop the hood and use the lever to shut it off every time -- it will rain cats and dogs every time you have to do this for at least a week.

Oil does nasty things to all the vac stuff, so don't wait.

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!