if it is stipped out then you need to apply upward pressure from under the bolt while using a high speed electric tool like a drill with a socket attached. then it should come right out
so maybe some large curved pliers with a socket under them so you can apply pressure while spinning it out.
unless that thing is totaly fubar I could have it out seconds
and if the metal insert is spinning as already mentioned then you need to apply both upward & downward pressure which could be done with the curved pliers and some kind of metal clip on the bottom of the pliers that fits around the bolt so when pressure is applied it holds the insert a little bit and gives you upward pressure at the same time.
I have taken worse things apart because I tend to strip bolts out, nothing is ever tight "enough" lol
