I Worked for Mercedes and Saw the W210s Every day
The Early W210s had the Dreaded 104 problems..But the late ones are MUCH better.......
O2 sensors ..
Leaking/defective cat converters
Mass air sensors..most of them fail because of over oiled air filters
Mono Belt tensioner
Lower control arm Bushings @60k
Seat frames Rocking/clicking
Window regulators...cheap Plastic
A/C Evap Temp Sensors...
The cars Havent had any oil Leak problems...yet!
The Trans are Good If The Trans fluid is Changed @30k No Lifetime Fluid!..same with The Diff and Coolant
The W210 Model year 2000 is Well Sorted ...Few Problems
I Enjoy My W210 wagon..Its been a Great car..so far