Today I cut the window frame in order to move it to where it needs to be.
It all bent into a far better position, so I clamped it all up dug the welder out, turned the gas on, and the wire fed, but it wouldn't strike an arc, not even a suggestion of anything, it was like I hadn't connected the earth (but I had)
So I stripped the welder down to find this

The earth kind of wasn't connected. So I used a jump lead as an earth strap and it welded really well, I think this has probably been an issue for a while.
Door frame rejoined

And ground back with a flap disc

I need to modify one of the shims to get the door to fit properly, but once I've done that I'll take some pictures of the finished result.
I am going to need to repaint the window frame, but such is life