I just changed plugs on 1998 ML320. I removed the frt wheels and the inner fender liner on both sides and it was an easy job. Replaced the frt pads also while wheels were off. you will get many answers on when to change them. I think time could be as important as miles. Also. one small exhaust shield needs to be removed on the drivers side. This is all easier than it sounds. I don't think my 1998 E320 wagon will be this easy. The ML had 89,000 miles. Good luck.