300SEL(W126)– spark plug change…?

Once again: Hello experts! Have you had any experience with the spark plug change? According to the boardbook, this should be done every 10,000Km. Do you have any other suggestions? P.S. How do I remove the soo fixed candle plugs? I use copper paste when twisting the new candles, or how firmly do I turn them without a torque wrench? Thank you in advance!