Don't know if this will help -- my Porsche had a reference in the owners manual as to how to move the power seat in the event the power went out. I havenít looked but perhaps MB has this same engineering feature? If nothing else you can try calling roadside assistance at 1-800-222-0100 and ask them. Last time I called, sorry to report, they were no da*n good...
BTW, this suggestion is based on the supposition that if you could reposition the power seat you could get at the bolt(s) causing this grief....
'00 ML320 "Casper"
'92 400E "Stella"