we have a 02 ML500 with around 187k on the clock, havent had issues yet with 1-4. Items I have replaced are:

brake pads
oil seals on the oil cooler and housing
CPS sensor
motor mounts
rack and pinion
passenger side CV joint [as the boot somehow got a tear in it....i think the shop who put the rack in tore it but i cant prove that even though it was gushing the day i got it back].

The truck does down shift hard every so often when coming to stops, will need to have fluids changed and such. I bought it from the dealer used, and it came with no service history records, just small stuff i could find on carfax, nothing beneficial My wife drive the truck a decent amount, its been a fairly good vehicle, plenty of power.