I am a little more down the purchase road then Charles as I bought the truck (2000 ML320 with 36K) about two weeks ago. After reading through this forum (great source of info) I compiled a list of things for the local MB dealer to check on (still have 6 months left on the factory warranty). My service appointment is tomorrow so I will post what they found/repaired soon so you have a better idea of what to expect. I bought the truck from Carmax which has a 5 day return policy which gives you time to take it to get it checked out at MB or a independent mech if you like. I bought the ML to replace my 89 Dodge Cavavan 4cyl which still runs like a top after 100K. My BMW has 155K and is just now getting tired. I have hopes the ML's life and service cost will take me at least into the 100K+ range.

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Slowdriver

2000 ML320 (37K Mi)
1985 BMW 735i (155K Mi)
1989 Caravan (102K Mi) cargo hauler
2000 Montana (40K Mi) family hauler