I had a 2000 ML320 that I purchased new and drove it for 86,000 miles. Only did normal maintenance on it with the exception of the Harmonic Balancer (replaced under recall campaign) and the Camshaft Position Sensor. When I traded it, I had never even replaced the brake pads. On the highway, I would get 27 mpg. I only sold it because I "fell in love" with a 2006 ML350 with AMG Design package on it that the Mercedes dealer had CPO'd. This car was previously owned by a local elderly gentlement who had 3 Mercedes vehicles and was told by his Doctor that he did not have long to live. The vehicle was his "toy" and was impeccably maintained. I have owned this vehicle for 2 years now with no issues during that time. The only thing I have done is change the oil and oil filter.

Judging form your experience, I probably could have kept my 2000 ML 320 for many more miles/years. However, I have really enjoyed my 2006 ML 350 as it drives much nicer, has more power and is quieter when driving down the highway.