How much trouble can one bolt be?

[Inspector]

How did you get it out?

Pete

 

[fenhayman]

Always remember that WD40 is not a penetrating fluid. Plus Gas is.

 

[Deadeye]

How did you get it out?

Pete

Impact driver after deepening the slot. To be honest all the other stuff may have helped, but the driver finally budged it

 

[valvebounce]

The best penetrating oil to use is automatic transmission fluid.Carefully drill a hole in it,and use a thread extractor in an electric impact driver.(in reverse)