Good evening friends of the S-class, soon my car will have the ASSYST A. Have looked at the work on WIS. It is manageable.The mileage is currently approx. 107000km. The spark plugs have not been changed to date, so the first ones are still ex works ( BJ 1999 ). When driving there are no irregularities to feel. Since 15000km I drive additionally with car gas ( LPG ). Also here no irregularities. Now my question: Is it useful to switch spark plugs just because it prescribes a service interval?I do not want to exchange a working part simply because it provides for some plan. It would be different if there were problems. I am curious about your opinions. Experiences about the standing times of the ignition plugs with your vehicles would be interesting for me. Note: I do not need answers like: S-class driving, but not able to entertain… etc. If I hadn’t been able to afford the S-Class, I would not have thought about it would have been a good thing to do for them.