I started to rewatch the whole series again, and couldn't help but notice there is actually one shot with a spot welder on the screen when the first piece of shiny door post going in, but immediately it has been replaced by a dozen plug welds. And richard did mention the reason the first panel had predrilled plug holes was the spot welder could not reach the location.

Thus i am suspecting using of plug welds might not be due to the childhood incident happened to nik, but some unsatisfactory result of the first plug weld, mind to share what had happened?