Re: spark plugs. I just had a 99 ML 320 at a dealer and I asked about maybe changing the plugs early (before 100K miles) to hopefully avoid avoid any seizing problem (by shortening the time in service). The service manager told me there were THREE plugs per cylinder, and it was an expensive job ($500) to replace them. He said that's why they don't recommend doing it earlier than the recommendation. He said they had had no problems with seizing.

I did an "are you sure?" number on him when he said 'three plugs' and he assured me that was right. I knew there were two, but what is the story on three?