Had the same problem on my 98 ML320 at about 55,000 miles - and one month after purchase from a private party. My mechanic broke several power wrenches trying to get the bolt off and ended up having to CUT it off. Thankfully he didnt' charge me the full amount of hours they spent on it.

At that point there was no evidence that the oil pan was cut into, but since then 10 miles later, a slight leak has appeared. I'm now on alert to watch the oil level. The dealer mechanic doesn't feel it's a problem, but we'll keep an eye on it.

Can't remember right now the other part that was ruined by the balancer being off, but that was another few hundred bucks too.

I wasn't able to take advantage of a "good will gesture" as I stupidly took it to my very accomplished Mercedes mechanic through whom I found the car.

I now only go to the local dealer for the ML.