Gordon is correct about the mice and spot weld cutter. I have a 1971 Dodge Challenger. When I bought it mice had been nesting in the wiper cowl area for years. Their urine had completely rotted out the firewall. I figured I could drill out the spot welds on the wiper cowl, sandblast the area, and weld in patches. But naturally it didn’t work out that way. The cowl had maybe thirty spot welds and I tried to be cheap and use Chinese spot weld cutters. They were advertised as M2 tool steel and were relatively inexpensive, but looked great. Each bit lasted for about six spot welds. When it became obvious I would have to remove the firewall itself I was looking at many more spot welds. I stepped up and got some American made bits, and what a difference it made. I only used one bit for the firewall, the roof, floor, deck filler, and trunk pans; must have been hundreds of spot welds easily.
If you want to see pics, here is a link to my photo album:
https://ImageEvent.com/adamell/wiperparts
Btw, I get a kick out of pics 235 & 236.