I guess with a Texas vehicle, rust isn't much of an issue...but I keep mine spotless, including the undercarriage. The lower panels may be treated, but they don't have the rough texture specific to undercoat material application.
I think MB tackled the rust issue marvelously, but my only cosmetic issue with the most recent offerings is their switching to the enviromentally-friendly water based paints...which succumbs to rock chips and debris easily. My 300E sees daily duty and doesn't have a tenth of the chipping I see on the ML (which does weekends and vacation duty mostly).
PHAEDRUS242 was pretty thorough about possible ML ails, but I would add that the transfer case issue had to do with the earlier units having a different gear ratio (60/40 vs 55/45, I believe).
Some dealers did the retrofit for free on the early units, but other than the shudder when making really hard parking-lot turns, there is no threat of transfer case failure as a result.
Most everything else PHAEDRUS242 mentioned has been isolated and corrected during my warranty period...usually performed all at once during my A or B service intervals.
No oil-related problems or leaks that I can tell, and I've had the ML on the synth plan since new.
I don't plan on getting rid of my ML for a later one, but I will have to admit that the newer versions have a better fit and finish (leather vs plastic door trim), rear seats are more comfortable, more safety items (door airbags and side curtains), and HID beams instead of halogen, and the NAV system and optional video playback system.
The exterior has been slightly modified to give the ML a more SUV-like appearance as opposed to a mini-van profile (as some have alluded).
Enjoy your possible purchase with relief knowing you've purchased an excellent vehicle in many respects.
