Just completed an overhaul of my fog lights and though I'd post experience. I don't think the old lights had been off in 30 years. Only way tio remove was to drill into the side of the nut, then bigger drill, then force to turn 2 flats, then repeat process of drilling, eventually splitting the nut.
I'd got a new pair of Fogs off Ebay, but it quickly became apparent the ball socket angle was wrong. Our cars need the mounting bolt to come square out of the back. The ones I'd got were at about 25 deg.
Initial plan was to therefore just use the glass and reflector, keeping the old back box. With careful filing, I removed the swagged staked corners from the rusty socket and was able to separate the bolt from the plastic for a better clean up.
After wire brushing and running a die down the old thread, I eventually had something I could re-use.
Then the thought dawned that I could remove the bolt from the new units, using that instead of the rusty old bits. Same filing of the stake's and the new back bowls in more bits than the designer intended.
But... The ball radius was different and would not clamp in the old plastic bowl.
So final step was to deepen the square slot in the new back bowl. Doesn't show too well in the photo below, but the one on the left is modified. Now the new bolt will go to the "square" setting on the new bowl, so finally, the whole of the fog light assembly is new. --- And I can swing it around on the ball socket to get a nice setting.
Tony
What goes together.... Must come apart.