...Another useful tip,when having to remove any type of fixing,is just to pop an M6 or M8 plain nut,over the head,and MIG or MMA in the centre...simply socket off.
The tiny inverter sets available,and a 1.6mm rod,sometimes are the easiest way round a couple of dozen gnarled heads.
Only mentioned this,as it reminded me of an incident at a large engineering works,years back.
I was there,sorting out some hydraulic issue,anywho...in the shop-floor managers' office,there was the foreman,and his 21 year old protege,attempting to remove the inner plate,off the back of a large,Chubb safe door.
It was secured with thirty+,countersunk,slotted screws,and they were seized proper. Drilling,warming and a centre punch,were not removing them...
I could sense an "unease" between the grumpy foreman,and his padawan...and when the former,sped off to find another impact driver,i wheeled the small shop MIG in,and showed the young lad how to weld a nut,and the socket,combined with the heat,had em' flying out.
The foreman returned,and the lad looked to me for an answer,which was "That lad of yours had an idea...hes' all over it..."
The foreman slunk off,Hilka impact in hand...the lad said "Thanks pal...that's proper done 'im"
Anyway...i'll get back to the sun-lounge...that jigsaw won't do itself...