If there's enough room on a 671 there's gotta be more than ample room on a 616. My bolts were pretty well stuck, too. I used a torque wrench to remove them set at 40 ft/lbs. That way if I applied more than that, it would click and I knew if I tried to go harder I'd break them off. Took a lot of heat, a lot of patience. Once I got them cracked loose I went back and forth many times spraying pb blaster on the threads and just working it in. I probably spent 2 hours getting all the bolts out. However that's way less time and effort than being hasty and breaking them off...

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1984 300TD -- summer daily driver
Many others that aren't Mercedes...