This time of year, when I see an older diesel for sale with new glow plugs, it usually is having starting problems.
Worn engine is usually the problem.

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79 240D my current toy
42 years a Diesel addict

240D sold
250SE sold
220D sold
280C sold
280S sold
300D (2) sold
300CD sold
300DT sold
300SD sold
380SL sold