Mine turns by hand, even with no power. Also, are you running the correct test? There is a Disc magnet test in the Diag section that engages the magnet in the spinner, that will make the thunk/jump thing your video is showing.

There is another test in the 1964 menu that spins the disc.

Not turning by hand means something is binding imo, either the disc is too tight to an edge and can't spin freely, something wrapped around the shaft, or the motor has seized.

That's my guess. Mine looks like it activates the magnet at the start and then spins the disc until you stop the test.

The pic you posted of the gear box in the motor looks the same as mine. I can't really get a useful picture without taking the whole mech out. I would look at the exploded picture in the manual and see if everything looks correct there. Pretty simple mechanism, motor, shaft, magnet so should be easy to eyeball and make sure nothing is rubbing.

There is also a small motor control board that could be the culprit, though that doesn't explain why the motor can't be spun by hand. When the game is on do you have lights on that board (small board just to the below and left of the motor when playfield is up)? Mine has a red led under the small fuse and a green led lit. If either of those are out the board or fuse on it could be bad.

Wasn’t suggesting the diagram would help take the motor apart. OP was asking for pics of underside of disc, I think the diagram is helpful in that context.

There is little to no value in them spending a lot of time trying to determine exactly where in the mech the problem is and sending you some some piece that you then have disassemble the mech and fix it yourself. They probably have built mechs sitting on a shelf behind them, they toss it in a box and away they go. It is an easy swap out, and if it still doesn't work for some reason at least there have been a lot of possibilities eliminated.

Just for shits and giggles, knowing you have a replacement part coming you could pull the whole mech out, disassemble and see if you can figure out exactly what went wrong, but I think their approach is the most efficient timewise for the both of you.

I get it. Sucks. The assumption that it would've been something they could've fixed over the phone if they would've just taken more time is not necessarily correct though. It is entirely possible the decision to send a new part was the only reasonable decision, and not sh*tty customer service. Just another perspective to consider.

As for charging you for the part, push back on that hard if it happens. Would be out of character for Stern to require that on a machine you just unboxed.