If replacing your plugs solves your problem, try to see what caused the plugs to foul in the first place.

Bad modulator?
valve guides/seals?

have a competent tech check it out!

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1939 170 - till I was 3, still turns heads
1989 300TE - daily driver has 263k
1987 300E - purrs happily with 120k
1983 300SD - keeps my friend happy