Mike, I don't think that those are what you would consider spot welds. They are more like concentrated solder joints. I've never seen one fail in a split bus panel, in fact I've seen more main breakers burn up than any split bus panel failure.
I miss them. I think that they afforded a lot of flexibility if installed properly. It was the end-user's lack of understanding that brought on their demise. That panel in the pictures was a work horse. I'll be that I installed 200 of them in their time in new home construction.
The only reason that we stopped using them is that we ran out of main breaker space when separate range and ovens got popular again. We had the heat, HWH, AC, dryer and range covered (plus the lighting main of course), but once we needed the seventh main breaker, our company switched over to main breaker panels even before they were required.
