My folks have a '99 ML320 which they bought new and speaking from a mechanic's point of view, the problems they experienced are nothing unusual to any early Mercedes model. Anything "major" was covered under warranty, and to be honest there really wasn't anything that was too "major". Mostly electrical glitches. I've serviced it with synthetic every 5K miles and they have kept up on all of the services, slicing normal recommendations in half to prolong the life of the vehicle and it has really been a great car (my mother drives it). I've actually got it in my shop as we speak for a minor service and tune up as they are leaving for Florida next week.

Looking back at it, I do recall one major repair, covered under warranty. That was the transfer case, a common problem on early models. That was right at 50K miles and it now has 116K with no problems since.

I'd advise you to only buy an early model if all of the updates and fixes have been completed and documented (i.e. transfer case, harmonic balancer, fuel filter mod, trip computer, etc...). It's also a bonus to have documented 5K fully synthetic oil changes, as I seem to recall that when I was at the dealer (when the ML was introduced) we were putting a lot of engines in them (in particular, over the sedans) because of MB's goof on the FSS 10K oil changes with dino goop.

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Regards,
Aaron