Thanks for the input.

Yes, I'd noticed the hex recess in the top end of the shock, but I'm missing any sort of nut that would fit in there, and MB have no information that suggests that one was ever installed. Perhaps the damper has more than one vehicle application.

I think I've ordered the correct replacement bolt (MA001 990 01 12), though I have my doubts. I could just source a button headed M6 torx bolt and a nyloc nut.

Cheers,

Krolroger