I remember that being somewhat of a bear to change on my '83 240D. I can't recall exactly, I would have to take a look, but I am pretty sure the bolt head was on the back of the cross member - it wasn't square though, just regular style. Although, there was this little metal retaining piece that swung over the bolt head. I didn't really understand it, but I guess it is there to keep the bolt from coming out should it ever loosen.

Anyway, I had the car up on ramps, and the way I got it to break free was to get a rachet on it so that the handle was pointing down towards the ground. Then, I slid my legs under the car from the driver's side and, while holding on tight to something underneath, I used my foot against the rachet handle to break it free. I was on tight and I knew I wasn't going to be able to break it with just my upper body strength in that cramped position.

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'95 E300D ("Tank") - 231,000 miles
'79 240D ("Biscuit") - 197,250 miles (Sold)
'83 240D ("Ding-Ding") - 217,000 miles (Death by deer)
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"Back off, man. I’m a scientist” ~ Peter Venkman