Greg,
A couple of points from a professionl MB mechanic. First of all do not attempt this job with a tool made in China or Taiwan. These tools are made of hardened butter. Once you round out that allen, you are screwed. Secondly the bolt is secured with blue Loc-Tite so heating the bolt with a smoke wrench will melt the Loc-Tite, but don't heat too mch or you will damage the front seal. Thirdly a good quality 1/2 inch impact will make the job a piece of cake if you have the room. ML320s have lots of room, but I don't know about your model.

Peter

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