Hardly anything about the ML "can't" be fixed, MB at least did come up with cures for most everything I can think of, except refusing to update the 50:50 transfer case on the first 500 or so (?) production models, but this was on the ML320 anyways, not the 430. The 430 I think were all pretty good, you don't even hear much about the oil consumption problem on the V8's like you do the V6, of course there are a lot more V6's out there.
If you want to avoid potential "quirks" in need of updating, buy the newest one you can afford.......
PS Personally I would NOT buy one with the Skyview Roof....rattles, leaks, motor problems, etc etc, NOT worth it unless you really really love it and won't mind the additional repair and upkeep.