For those of you that summarily disclaim Zinsco panels with the blanket “replacement” recommendation, this may not mean anything to you.
But for the rest of us, do you see the defect?
The right extension connection tab is missing?
Did I win?
Nope. Try again.
If you have any pictures of these panels, take a look at them. Once you see it, you can’t not see it.
A nail…
I don’t see them often at all…an old house here is 1985…but the right connection tab is broken. Look for yourself.
That “black” thing is a Mylar backing installed in Zinsco panels to prevent contact between the bus bars and the panel enclosure.
I won’t say much more just yet.
There’s a nail about to kill someone?
Wires going across the back of the breakers?
No. It’s looking you square in the face in both pictures.
Here are a couple to compare to. Not the best examples, but it may help.
Is that exposed bus sticking out the ends unprotected?
Retaining clip / block is missing at both ends of bus bars.
Yes. But the defect is that the stand-offs have been removed (that’s why the ends of the bus bars have been exposed).
Someone decided they needed just a bit more room for breakers, so they pulled out the stand-offs.
Steve - I knew you would see it 
I just saw the defect in my phone. I saw the missing parts right away.
These are crucial components. The fact that they were removed just blows me away.
Thanks Jeff. I’ve never seen on of these panels. Now I know.
By the way. Your pictures are a good illustration of how pictures should be taken. If you have the correct narrative you don’t have to have arrows, circles or anything else to highlight the defect.
That’s how I roll. I don’t add arrows or circles to any of my report pictures. 
Exceptional post Jeff and great catch.