Jeffrey, I have 99 ML430 since new with 90,000 now. I follow FSS intervals - comes usualy at 12,000. I always do my own oil change, use M1 15W50. Recently I sent oil to the lab after 6000 miles and the result was very good, almost as new oil, no change needed. Once in the past I went NY to AK and back with no oil change, so I had almost 15000 on the oil and FSS indicated I had more oil life left. Here is a comparison of the lab results:

After 6k miles................ After 15k miles
Aluminum 5...........................7
Chromium 1..........................1
Iron 12 ...........................16
Copper 4...............................7
Lead 0...................................4
Tin 1 ....................................1
Molibden 0.............................0
Nickel 2..................................0
Manganese 3 ......................72*
Silver 0 ..................................0
Titanium 0............................. 0
Potassium 9...........................0
Boron 58..............................31
Silicon 23...............................9
Sodium 5................................4

* High Manganese content was due to a lot of Canadian gas used
Regards, Mike