Hello ,

I went to a tool store and bought the largest flat blade screwdriver I could find that would fit. A lot of cloth around the butt and gently held it in a vice.
I then used a a large adjustable spanner on the screwdriver handle for extra leverage - Bobs your Aunt and the bolt came out.
WD40 ? Great on wet/damp electrical stuff. I'd use parafin or diesel myself.

Just my thoughts .

Regards,

Sam