Sadly, our '99 ML320 was the worst Benz we've ever owned (oddly one of the best is the current '90 W124 with a hair under 200k on the clock). Gorgeous in black with all the exterior factory bling (we bought it used in 2001 with 16k on the odo).
After the traction control lights would not go off, and we started getting a number of O2 sensor CEL's (that would then go away again after a few days - it was time to trade her in). It was an exceptional off-road machine with the electronic traction control (last time we tested it was on a beach and it was unstoppable).
Now, it's W124's for this family. Should have another delivered tomorrow weather permitting.
Some of the things I recall us having to fix on the ML
Accel cable (was sticky.. scary!)
brake light switch
brakes (pads and rotors twice in the first 50k miles)
rear hatch bagan to rattle, never was able to resolve that
I can't recall all the little things but I spent more time ordering parts from Faslane for the ML than I did for the much older 300E. I wanted to love it but secretly I'm glad the wife agreed to sell it, I was getting scared that we were on the verge of a HUGE repair bill...