To remove a stuck bolt try this-
Drill/Cut off its head as needed to drill and then tap a left hand thread inside.
Insert a left hand thread bolt and tighten up.
The direction that tightens the new bolt is the loosening direction of the old bolt.
There is some skill in choosing the size and drilling along the centre and aligning. Choose a thread size and head for the left hand bolt that enables you to get a big spanner on it.
-rubberbudgie- you may be past that, sometimes you can drill the stuck bolt and the remnants still won't come out, then you have drill even more and remove the case material and rethread with a bigger size bolt or an insert.